Calorimetric method of ac loss measurement in a rotating magnetic field.
Ghoshal, P K; Coombs, T A; Campbell, A M
2010-07-01
A method is described for calorimetric ac-loss measurements of high-T(c) superconductors (HTS) at 80 K. It is based on a technique used at 4.2 K for conventional superconducting wires that allows an easy loss measurement in parallel or perpendicular external field orientation. This paper focuses on ac loss measurement setup and calibration in a rotating magnetic field. This experimental setup is to demonstrate measuring loss using a temperature rise method under the influence of a rotating magnetic field. The slight temperature increase of the sample in an ac-field is used as a measure of losses. The aim is to simulate the loss in rotating machines using HTS. This is a unique technique to measure total ac loss in HTS at power frequencies. The sample is mounted on to a cold finger extended from a liquid nitrogen heat exchanger (HEX). The thermal insulation between the HEX and sample is provided by a material of low thermal conductivity, and low eddy current heating sample holder in vacuum vessel. A temperature sensor and noninductive heater have been incorporated in the sample holder allowing a rapid sample change. The main part of the data is obtained in the calorimetric measurement is used for calibration. The focus is on the accuracy and calibrations required to predict the actual ac losses in HTS. This setup has the advantage of being able to measure the total ac loss under the influence of a continuous moving field as experienced by any rotating machines.
21 CFR 886.4440 - AC-powered magnet.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false AC-powered magnet. 886.4440 Section 886.4440 Food... DEVICES OPHTHALMIC DEVICES Surgical Devices § 886.4440 AC-powered magnet. (a) Identification. An AC-powered magnet is an AC-powered device that generates a magnetic field intended to find and remove...
NASA Astrophysics Data System (ADS)
Cao, Yongze; Kumar, Pawan; Zhao, Yue; Yoshimura, Satoru; Saito, Hitoshi
2018-05-01
Understanding the dynamic magnetization process of magnetic materials is crucial to improving their fundamental properties and technological applications. Here, we propose active magnetic force microscopy for observing reversible and irreversible magnetization processes by stimulating magnetization with an AC magnetic field based on alternating magnetic force microscopy with a sensitive superparamagnetic tip. This approach simultaneously measures sample's DC and AC magnetic fields. We used this microscopy approach to an anisotropic Sr-ferrite (SrF) sintered magnet. This is a single domain type magnet where magnetization mainly changes via magnetic rotation. The proposed method can directly observe the reversible and irreversible magnetization processes of SrF and clearly reveal magnetic domain evolution of SrF (without stimulating magnetization—stimulating reversible magnetization—stimulating irreversible magnetization switching) by slowly increasing the amplitude of the external AC magnetic field. This microscopy approach can evaluate magnetic inhomogeneity and explain the local magnetic process within the permanent magnet.
NASA Astrophysics Data System (ADS)
Kase, Aina; Akagi, Fumiko; Yoshida, Kazuetsu
2018-05-01
Microwave assisted magnetic recording (MAMR) is a promising recording method for achieving high recording densities in hard disk drives. In MAMR, the AC field from a spin-torque oscillator (STO) assists the head field with magnetization reversal in a medium. Therefore, the relationship between the head field and the AC field is very important. In this study, the effects of the head field and the AC field on magnetization reversal were analyzed using a micromagnetic simulator that takes the magnetic interactions between a single-pole type (SPT) write-head, an exchange coupled composite (ECC) medium, and the STO into account. As a result, the magnetization reversal was assisted not just by the y-component of the AC field (Hstoy) but also by the y-component of the head field (Hhy) in the medium. The Hhy over 100 kA/m with a frequency of about 15.5 GHz induced the magnetic resonance. The large Hhy was produced by the field from the STO to the SPT head.
Characterizing superconducting thin films using AC Magnetic Susceptibility
NASA Astrophysics Data System (ADS)
Mahoney, C. H.; Porzio, J.; Sullivan, M. C.
2014-03-01
We present our work on using ac magnetic susceptibility to determine the critical temperature of superconducting thin films. In ac magnetic susceptibility, the thin film is placed between two coils. One coil carries an ac signal, creating a varying external magnetic field. We measure the voltage induced in the pick-up coil on the opposite side of the sample and measure how the sample magnetization changes as the temperature changes. We will present our work to use ac susceptibility to determine critical temperature and superconducting volume fraction. Using our own analysis program, we are able to accurately locate the critical temperatures of the samples and determine the transition width. For the superconducting volume fraction, we etch samples in order to control the thicknesses of the sample and measure how much of the material grown on the surface is superconducting. Supported by NFS grant DMR-1305637.
SQUIDs De-fluxing Using a Decaying AC Magnetic Field
DOE Office of Scientific and Technical Information (OSTI.GOV)
Matlashov, Andrei Nikolaevich; Semenov, Vasili Kirilovich; Anderson, Bill
Flux trapping is the Achilles’ heel of all superconductor electronics. The most direct way to avoid flux trapping is a prevention of superconductor circuits from exposure to magnetic fields. Unfortunately this is not feasible if the circuits must be exposed to a strong DC magnetic field even for a short period of time. For example, such unavoidable exposures take place in superparamagnetic relaxation measurements (SPMR) and ultra-low field magnetic resonance imaging (ULF MRI) using unshielded thin-film SQUID-based gradiometers. Unshielded SQUIDs stop working after being exposed to DC magnetic fields of only a few Gauss in strength. In this paper wemore » present experimental results with de-fluxing of planar thin-film LTS SQUID-based gradiometers using a strong decaying AC magnetic field. We used four commercial G136 gradiometers for SPMR measurements with up to a 10 mT magnetizing field. Strong 12.9 kHz decaying magnetic field pulses reliably return SQUIDs to normal operation 50 ms after zeroing the DC magnetizing field. This new AC de-fluxing method was also successfully tested with seven other different types of LTS SQUID sensors and has been shown to dissipate extremely low energy.« less
A magnetic-piezoelectric smart material-structure sensing three axis DC and AC magnetic-fields
NASA Astrophysics Data System (ADS)
Hung, Chiao-Fang; Chen, Chin-Chung; Yeh, Po-Chen; Chen, Po-Wen; Chung, Tien-Kan
2017-12-01
In this paper, we demonstrate a smart material-structure can sense not only three-axis AC magnetic-fields but also three-axis DC magnetic-fields. Under x-axis and z-axis AC magnetic field ranging from 0.2 to 3.2 gauss, sensing sensitivity of the smart material-structure stimulated at resonant frequency is approximate 8.79 and 2.80 mV/gauss, respectively. In addition, under x-axis and z-axis DC magnetic fields ranging from 2 to 12 gauss, the sensitivity of the smart material-structure is 1.24-1.54 and 1.25-1.41 mV/gauss, respectively. In addition, under x-axis and z-axis DC magnetic fields ranging from 12 to 20 gauss, the sensitivity of the smart material-structure is 5.17-6.2 and 3.97-4.57 mV/gauss, respectively. These experimental results show that the smart material-structure successfully achieves three-axis DC and AC magnetic sensing as we designed. Furthermore, we also compare the results of the AC and DC magnetic-field sensing to investigate discrepancies. Finally, when applying composite magnetic-fields to the smart material-structure, the smart material-structure shows decent outputs as expected (consistent to the sensing principle). In the future, we believe the smart material-structure capable of sensing AC and DC magnetic fields will have more applications than conventional structures capable of sensing only DC or AC magnetic field. Thus, the smart material-structure will be an important design reference for future magnetic-field sensing technologies.
NASA Astrophysics Data System (ADS)
Falqueiro, A. M.; Siqueira-Moura, M. P.; Jardim, D. R.; Primo, F. L.; Morais, P. C.; Mosiniewicz-Szablewska, E.; Suchocki, P.; Tedesco, A. C.
2012-04-01
The goals of this study are to evaluate invitro compatibility of magnetic nanomaterials and their therapeutic potential against cancer cells. Highly stable ionic magnetic fluid sample (maghemite, γ-Fe2O3) and Selol were incorporated into polymeric nanocapsules by nanoprecipitation method. The cytotoxic effect of Selol-loaded magnetic nanocapsules was assessed on murine melanoma (B16-F10) and oral squamous cell carcinoma (OSCC) cell lines following AC magnetic field application. The influence of different nanocapsules on cell viability was investigated by colorimetric MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. In the absence of AC magnetic field Selol-loaded magnetic nanocapsules, containing 100 µg/mL Selol plus 5 × 1012 particle/mL, showed antitumoral activity of about 50% on B16-F10 melanoma cells while OSCC carcinoma cells demonstrated drug resistance at all concentrations of Selol and magnetic fluid (range of 100-500 µg/mL Selol and 5 × 1012-2.5 × 1013 particle/mL). On the other hand, under AC applied fields (1 MHz and 40 Oe amplitude) B16-F10 cell viability was reduced down to 40.5% (±3.33) at the highest concentration of nanoencapsulated Selol. The major effect, however, was observed on OSCC cells since the cell viability drops down to about 33.3% (±0.38) under application of AC magnetic field. These findings clearly indicate that the Selol-loaded magnetic nanocapsules present different toxic effects on neoplastic cell lines. Further, the cytotoxic effect was maximized under AC magnetic field application on OSCC, which emphasizes the effectiveness of the magnetohyperthermia approach.
AC magnetic-field response of the ferromagnetic superconductor UGe2 with different magnetized states
NASA Astrophysics Data System (ADS)
Tanaka, Hiroyuki; Yamaguchi, Akira; Kawasaki, Ikuto; Sumiyama, Akihiko; Motoyama, Gaku; Yamamura, Tomoo
2018-01-01
We have performed parallel measurements of dc-magnetization and ac-magnetic susceptibility for a ferromagnetic superconductor, UGe2, in the ferromagnetic-superconducting phase. dc-magnetization measurements revealed that adequate demagnetizing of the sample allows for the preparation of various magnetized states with different zero-field residual magnetization. We observed that these states exhibit varying ac superconducting response at large ac-field amplitudes. The amount of ac flux penetration is less in the demagnetized state involving many domain walls. This result seems to contradict the theory that considers the domain walls as weak links. Moreover, the ferromagnetic domain walls enforce the shielding capability of superconductivity. This observation sheds light on the role of the domain walls on superconductivity, which has been a controversial issue for several decades. Two possible scenarios are presented to explain the enhancement of the shielding capability by the domain walls.
NASA Astrophysics Data System (ADS)
Zhou, Jianxin; Kang, Wen; Li, Shuai; Liu, Yudong; Liu, Yiqin; Xu, Shouyan; Guo, Xiaoling; Wu, Xi; Deng, Changdong; Li, Li; Wu, Yuwen; Wang, Sheng
2018-02-01
The China Spallation Neutron Source (CSNS) has two major accelerator systems, a linear accelerator and a rapid cycling synchrotron (RCS). The RCS accelerator is used to accumulate and accelerate protons from the energy of 80 MeV to the design energy of 1.6 GeV at the repetition rate of 25 Hz, and extract the high energy beam to the target. The main magnets of the RCS accelerator are excited by AC current with DC bias. The magnetic field quality is very important for the RCS accelerator operation, since it should guarantee and focus a circulating beam. In order to characterize the AC magnets, a small flip coil measurement system has been developed and one of each type of AC magnets has been studied. The measurement system and selected measurement results are presented in this paper.
NASA Astrophysics Data System (ADS)
Robert, B. C.; Ruiz, H. S.
2018-07-01
Remarkable features on the magnetic moment of type-II superconducting (SC) wires of cylindrical shape, subjected to direct current conditions (DC) and transverse oscillating (AC) magnetic fields, are reported. We show how for relatively low amplitudes of the applied magnetic field, B a , the superconducting wire rapidly develops a saturation state, | {M}p| , characterizing the limits of magnetization loops that exhibit a Boolean-like behaviour. Regardless of the premagnetization state of the SC wire, we show how after two cycles of magnetic relaxation, boolean-like ±M p states can be measured during the entire period of time from which the external magnetic field B 0 ranges from 0 to ±B a , with the signs rule defined by the sign of the slope ΔB 0y (t). In addition, for the practical implementation of SC DC wires sharing the right of way with AC lines, we report that for relatively low values of magnetic field, {B}a≤slant {B}P/2, being B P the analytical value for the full penetration field in absence of transport current, I tr, the use of semi-analytical approaches for the calculation of AC losses leads to a significant underestimation of the actual contribution of the induction losses. This phenomena is particularly relevant at dimensionless fields {b}a< 1-{i}a2/3, being b a = B a /B P and, i a = I a /I c the amplitude of an AC or DC transport current, due to the local motion of flux front profiles being dominated by the occurrence of transport current. On the other hand, we have found that regardless of the nature of the transport current, either be DC or AC, when a transverse oscillating magnetic field greater than the classical limit b a = (1 - i a ) is applied to the SC wire, the difference between the obtained AC losses in both situations results to be negligible indistinctly of the approach used, semi-analytical or numerical. Thus, the actual limits from which the estimation of the AC losses can be used as an asset for the deployment of DC SC wires
Corá, Luciana A; Romeiro, Fernando G; Américo, Madileine F; Oliveira, Ricardo Brandt; Baffa, Oswaldo; Stelzer, Murilo; Miranda, José Ricardo de Arruda
2006-01-01
The oral administration is a common route in the drug therapy and the solid pharmaceutical forms are widely used. Although much about the performance of these formulations can be learned from in vitro studies using conventional methods, evaluation in vivo is essential in product development. The knowledge of the gastrointestinal transit and how the physiological variables can interfere with the disintegration and drug absorption is a prerequisite for development of dosage forms. The aim of this work was to employing the ac biosusceptometry (ACB) to monitoring magnetic tablets in the human gastrointestinal tract and to obtain the magnetic images of the disintegration process in the colonic region. The ac biosusceptometry showed accuracy in the quantification of the gastric residence time, the intestinal transit time and the disintegration time (DT) of the magnetic formulations in the human gastrointestinal tract. Moreover, ac biosusceptometry is a non-invasive technique, radiation-free and harmless to the volunteers, as well as an important research tool in the pharmaceutical, pharmacological and physiological investigations.
NASA Astrophysics Data System (ADS)
Kajikawa, K.; Funaki, K.; Shikimachi, K.; Hirano, N.; Nagaya, S.
2010-11-01
AC losses in a superconductor strip are numerically evaluated by means of a finite element method formulated with a current vector potential. The expressions of AC losses in an infinite slab that corresponds to a simple model of infinitely stacked strips are also derived theoretically. It is assumed that the voltage-current characteristics of the superconductors are represented by Bean's critical state model. The typical operation pattern of a Superconducting Magnetic Energy Storage (SMES) coil with direct and alternating transport currents in an external AC magnetic field is taken into account as the electromagnetic environment for both the single strip and the infinite slab. By using the obtained results of AC losses, the influences of the transport currents on the total losses are discussed quantitatively.
Cao, Yongze; Nakayama, Shota; Kumar, Pawan; Zhao, Yue; Kinoshita, Yukinori; Yoshimura, Satoru; Saito, Hitoshi
2018-05-03
For magnetic domain imaging with a very high spatial resolution by magnetic force microscopy the tip-sample distance should be as small as possible. However, magnetic imaging near sample surface is very difficult with conventional MFM because the interactive forces between tip and sample includes van der Waals and electrostatic forces along with magnetic force. In this study, we proposed an alternating magnetic force microscopy (A-MFM) which extract only magnetic force near sample surface without any topographic and electrical crosstalk. In the present method, the magnetization of a FeCo-GdOx superparamagnetic tip is modulated by an external AC magnetic field in order to measure the magnetic domain structure without any perturbation from the other forces near the sample surface. Moreover, it is demonstrated that the proposed method can also measure the strength and identify the polarities of the second derivative of the perpendicular stray field from a thin-film permanent magnet with DC demagnetized state and remanent state. © 2018 IOP Publishing Ltd.
Electroporation of cells using EM induction of ac fields by a magnetic stimulator
NASA Astrophysics Data System (ADS)
Chen, C.; Evans, J. A.; Robinson, M. P.; Smye, S. W.; O'Toole, P.
2010-02-01
This paper describes a method of effectively electroporating mammalian cell membranes with pulsed alternating-current (ac) electric fields at field strengths of 30-160 kV m-1. Although many in vivo electroporation protocols entail applying square wave or monotonically decreasing pulses via needles or electrode plates, relatively few have explored the use of pulsed ac fields. Following our previous study, which established the effectiveness of ac fields for electroporating cell membranes, a primary/secondary coil system was constructed to produce sufficiently strong electric fields by electromagnetic induction. The primary coil was formed from the applicator of an established transcranial magnetic stimulation (TMS) system, while the secondary coil was a purpose-built device of a design which could eventually be implanted into tissue. The effects of field strength, pulse interval and cumulative exposure time were investigated using microscopy and flow cytometry. Results from experiments on concentrated cell suspensions showed an optimized electroporation efficiency of around 50%, demonstrating that electroporation can be practicably achieved by inducing such pulsed ac fields. This finding confirms the possibility of a wide range of in vivo applications based on magnetically coupled ac electroporation.
NASA Astrophysics Data System (ADS)
Brandt, Ernst Helmut
1998-09-01
The ac susceptibility χ=χ'-iχ'' of superconductor cylinders of finite length in a magnetic field applied along the cylinder axis is calculated using the method developed in the preceding paper, part I. This method does not require any approximation of the infinitely extended magnetic field outside the cylinder or disk but directly computes the current density J inside the superconductor. The material is characterized by a general current-voltage law E(J), e.g., E(J)=Ec[J/Jc(B)]n(B), where E is the electric field, B=μ0H the magnetic induction, Ec a prefactor, Jc the critical current density, and n>=1 the creep exponent. For n>1, the nonlinear ac susceptibility is calculated from the hysteresis loops of the magnetic moment of the cylinder, which is obtained by time integration of the equation for J(r,t). For n>>1 these results go over into the Bean critical state model. For n=1, and for any linear complex resistivity ρac(ω)=E/J, the linear ac susceptibility is calculated from an eigenvalue problem which depends on the aspect ratio b/a of the cylinder or disk. In the limits b/a<<1 and b/a>>1, the known results for thin disks in a perpendicular field and long cylinders in a parallel field are reproduced. For thin disks in a perpendicular field, at large frequencies χ(ω) crosses over to the behavior of slabs in parallel geometry since the magnetic field lines are expelled and have to flow around the disk. The results presented may be used to obtain the nonlinear or linear resistivity from contact-free magnetic measurements on superconductors of realistic shape.
NASA Astrophysics Data System (ADS)
Jordan, Andreas; Scholz, Regina; Wust, Peter; Fähling, Horst; Felix, Roland
1999-07-01
The story of hyperthermia with small particles in AC magnetic fields started in the late 1950s, but most of the studies were unfortunately conducted with inadequate animal systems, inexact thermometry and poor AC magnetic field parameters, so that any clinical implication was far behind the horizon. More than three decades later, it was found, that colloidal dispersions of superparamagnetic (subdomain) iron oxide nanoparticles exhibit an extraordinary specific absorption rate (SAR [ W/ g]), which is much higher at clinically tolerable H 0 f combinations in comparison to hysteresis heating of larger multidomain particles. This was the renaissance of a cancer treatment method, which has gained more and more attention in the last few years. Due to the increasing number of randomized clinical trials preferentially in Europe with conventional E-field hyperthermia systems, the general medical and physical experience in hyperthermia application is also rapidly growing. Taking this increasing clinical experience carefully into account together with the huge amount of new biological data on heat response of cells and tissues, the approach of magnetic fluid hyperthermia (MFH) is nowadays more promising than ever before. The present contribution reviews the current state of the art and some of the future perspectives supported by advanced methods of the so-called nanotechnology.
Note: A phase synchronization photography method for AC discharge.
Wu, Zhicheng; Zhang, Qiaogen; Ma, Jingtan; Pang, Lei
2018-05-01
To research discharge physics under AC voltage, a phase synchronization photography method is presented. By using a permanent-magnet synchronous motor to drive a photography mask synchronized with a discharge power supply, discharge images in a specific phase window can be recorded. Some examples of discharges photographed by this method, including the corona discharge in SF 6 and the corona discharge along the air/epoxy surface, demonstrate the feasibility of this method. Therefore, this method provides an effective tool for discharge physics researchers.
Note: A phase synchronization photography method for AC discharge
NASA Astrophysics Data System (ADS)
Wu, Zhicheng; Zhang, Qiaogen; Ma, Jingtan; Pang, Lei
2018-05-01
To research discharge physics under AC voltage, a phase synchronization photography method is presented. By using a permanent-magnet synchronous motor to drive a photography mask synchronized with a discharge power supply, discharge images in a specific phase window can be recorded. Some examples of discharges photographed by this method, including the corona discharge in SF6 and the corona discharge along the air/epoxy surface, demonstrate the feasibility of this method. Therefore, this method provides an effective tool for discharge physics researchers.
21 CFR 886.4440 - AC-powered magnet.
Code of Federal Regulations, 2014 CFR
2014-04-01
... metallic foreign bodies from eye tissue. (b) Classification. Class II. ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false AC-powered magnet. 886.4440 Section 886.4440 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL...
21 CFR 886.4440 - AC-powered magnet.
Code of Federal Regulations, 2012 CFR
2012-04-01
... metallic foreign bodies from eye tissue. (b) Classification. Class II. ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false AC-powered magnet. 886.4440 Section 886.4440 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL...
21 CFR 886.4440 - AC-powered magnet.
Code of Federal Regulations, 2011 CFR
2011-04-01
... metallic foreign bodies from eye tissue. (b) Classification. Class II. ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false AC-powered magnet. 886.4440 Section 886.4440 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL...
21 CFR 886.4440 - AC-powered magnet.
Code of Federal Regulations, 2013 CFR
2013-04-01
... metallic foreign bodies from eye tissue. (b) Classification. Class II. ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false AC-powered magnet. 886.4440 Section 886.4440 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL...
Testing of a First Order AC Magnetic Susceptometer
NASA Astrophysics Data System (ADS)
Fukuda, Ryan; Sunny, Smitha; Ho, Pei-Chun
2011-11-01
A first-order AC magnetic susceptometer has been constructed and tested to find the magnetic response of strongly correlated electron materials. The instrument works by using a primary coil to apply a small AC magnetic field of .104 Oe to a sample with a cylindrical coil space of length .635 cm and diameter .355 cm. A lock-in amplifier is used to monitor the induced voltage from a set of secondary coils. By coupling a temperature-controlled system with this instrument, the change in the magnetic signal with respect to temperature is measured. Monitoring the signal changes may indicate the temperature that causes the material to transition to either a ferromagnetic, anti-ferromagnetic, or superconducting state. A 122.47 mg Gd polycrystal was used to test our susceptometer. The data qualitatively agrees with the previous results of magnetization vs. temperature of Gd single crystals by Nigh et al. [1]: there is a steep increase in the pick-up signal at 300 K where Gd becomes ferromagnetic and a peak at 210 K [1]. This susceptometer will be used for our future investigation of magnetic properties of rare earth compounds and nanoparticles in the temperature range of 10 K to 300 K. [4pt] [1] H. E. Nigh, S. Legvold, and F. H. Spedding, Physical Review 132, 1092 (1963)
Suzuki, Masashi; Aki, Atsushi; Mizuki, Toru; Maekawa, Toru; Usami, Ron; Morimoto, Hisao
2015-01-01
We propose a method of activating an enzyme utilizing heat generation from ferromagnetic particles under an ac magnetic field. We immobilize α-amylase on the surface of ferromagnetic particles and analyze its activity. We find that when α-amylase/ferromagnetic particle hybrids, that is, ferromagnetic particles, on which α-amylase molecules are immobilized, are subjected to an ac magnetic field, the particles generate heat and as a result, α-amylase on the particles is heated up and activated. We next prepare a solution, in which α-amylase/ferromagnetic particle hybrids and free, nonimmobilized chitinase are dispersed, and analyze their activities. We find that when the solution is subjected to an ac magnetic field, the activity of α-amylase immobilized on the particles increases, whereas that of free chitinase hardly changes; in other words, only α-amylase immobilized on the particles is selectively activated due to heat generation from the particles.
The DC and AC insulating properties of magnetic fluids based on transformer oil
NASA Astrophysics Data System (ADS)
Tomo, L.; Marton, K.; Herchl, F.; Kopanský, P.; Potoová, I.; Koneracká, M.; Timko, M.
2006-01-01
The AC-dielectric breakdown was investigated in magnetic fluids based on transformer oil TECHNOL US 4000 for two orientations of external magnetic field (B E and B E) and in B = 0. The found results were compared with those obtained formerly for the DC-dielectric breakdown. The observations of the time development of the AC-dielectric breakdown showed the presence of partial discharges long before the complete breakdown occurrence, while for DC-dielectric breakdown a complete breakdown of the gap next to the onset of a measurable ionization was characteristic. The comparison of the AC-dielectric breakdown strengths of pure transformer oil and transformer-oil-based magnetic fluid showed better dielectric properties of magnetic fluid in external magnetic field and comparable, but not worse, in B = 0. Regarding to the better heat transfer, provided by magnetic fluids, they could be used in power transformers as insulating fluids.
Spectroscopic AC Susceptibility Imaging (sASI) of Magnetic Nanoparticles
Ficko, Bradley W.; Nadar, Priyanka M.; Diamond, Solomon G.
2014-01-01
This study demonstrates a method for alternating current (AC) susceptibility imaging (ASI) of magnetic nanoparticles (mNPs) using low cost instrumentation. The ASI method uses AC magnetic susceptibility measurement to create tomographic images using an array of drive coils, compensation coils and fluxgate magnetometers. Using a spectroscopic approach in conjunction with ASI, a series of tomographic images can be created for each frequency measurement and is termed sASI. The advantage of sASI is that mNPs can be simultaneously characterized and imaged in a biological medium. System calibration was performed by fitting the in-phase and out-of-phase susceptibility measurements of an mNP sample with a hydrodynamic diameter of 100 nm to a Brownian relaxation model (R2 = 0.96). Samples of mNPs with core diameters of 10 and 40 nm and a sample of 100 nm hydrodynamic diameter were prepared in 0.5 ml tubes. Three mNP samples were arranged in a randomized array and then scanned using sASI with six frequencies between 425 and 925 Hz. The sASI scans showed the location and quantity of the mNP samples (R2 = 0.97). Biological compatibility of the sASI method was demonstrated by scanning mNPs that were injected into a pork sausage. The mNP response in the biological medium was found to correlate with a calibration sample (R2 = 0.97, p <0.001). These results demonstrate the concept of ASI and advantages of sASI. PMID:25477704
Suzuki, Masashi; Aki, Atsushi; Mizuki, Toru; Maekawa, Toru; Usami, Ron; Morimoto, Hisao
2015-01-01
We propose a method of activating an enzyme utilizing heat generation from ferromagnetic particles under an ac magnetic field. We immobilize α-amylase on the surface of ferromagnetic particles and analyze its activity. We find that when α-amylase/ferromagnetic particle hybrids, that is, ferromagnetic particles, on which α-amylase molecules are immobilized, are subjected to an ac magnetic field, the particles generate heat and as a result, α-amylase on the particles is heated up and activated. We next prepare a solution, in which α-amylase/ferromagnetic particle hybrids and free, nonimmobilized chitinase are dispersed, and analyze their activities. We find that when the solution is subjected to an ac magnetic field, the activity of α-amylase immobilized on the particles increases, whereas that of free chitinase hardly changes; in other words, only α-amylase immobilized on the particles is selectively activated due to heat generation from the particles. PMID:25993268
Hung, Chiao-Fang; Yeh, Po-Chen; Chung, Tien-Kan
2017-02-08
In this paper, we demonstrate a miniature magnetic-force-based, three-axis, AC magnetic sensor with piezoelectric/vibrational energy-harvesting functions. For magnetic sensing, the sensor employs a magnetic-mechanical-piezoelectric configuration (which uses magnetic force and torque, a compact, single, mechanical mechanism, and the piezoelectric effect) to convert x -axis and y -axis in-plane and z -axis magnetic fields into piezoelectric voltage outputs. Under the x -axis magnetic field (sine-wave, 100 Hz, 0.2-3.2 gauss) and the z -axis magnetic field (sine-wave, 142 Hz, 0.2-3.2 gauss), the voltage output with the sensitivity of the sensor are 1.13-26.15 mV with 8.79 mV/gauss and 1.31-8.92 mV with 2.63 mV/gauss, respectively. In addition, through this configuration, the sensor can harness ambient vibrational energy, i.e., possessing piezoelectric/vibrational energy-harvesting functions. Under x -axis vibration (sine-wave, 100 Hz, 3.5 g) and z -axis vibration (sine-wave, 142 Hz, 3.8 g), the root-mean-square voltage output with power output of the sensor is 439 mV with 0.333 μW and 138 mV with 0.051 μW, respectively. These results show that the sensor, using this configuration, successfully achieves three-axis magnetic field sensing and three-axis vibration energy-harvesting. Due to these features, the three-axis AC magnetic sensor could be an important design reference in order to develop future three-axis AC magnetic sensors, which possess energy-harvesting functions, for practical industrial applications, such as intelligent vehicle/traffic monitoring, processes monitoring, security systems, and so on.
NASA Astrophysics Data System (ADS)
Glowacki, B. A.; Majoros, M.
2009-06-01
Magnetic materials can help to improve the performance of practical superconductors on the macroscale/microscale as magnetic diverters and also on the nanoscale as effective pinning centres. It has been established by numerical modelling that magnetic shielding of the filaments reduces AC losses in self-field conditions due to decoupling of the filaments and, at the same time, it increases the critical current of the composite. This effect is especially beneficial for coated conductors, in which the anisotropic properties of the superconductor are amplified by the conductor architecture. However, ferromagnetic coatings are often chemically incompatible with YBa2Cu3O7 and (Pb,Bi)2Sr2Ca2Cu3O9 conductors, and buffer layers have to be used. In contrast, in MgB2 conductors an iron matrix may remain in direct contact with the superconducting core. The application of superconducting-magnetic heterostructures requires consideration of the thermal and electromagnetic stability of the superconducting materials used. On one hand, magnetic materials reduce the critical current gradient across the individual filaments but, on the other hand, they often reduce the thermal conductivity between the superconducting core and the cryogen, which may cause destruction of the conductor in the event of thermal instability. A possible nanoscale method of improving the critical current density of superconducting conductors is the introduction of sub-micron magnetic pinning centres. However, the volumetric density and chemical compatibility of magnetic inclusions has to be controlled to avoid suppression of the superconducting properties.
Hung, Chiao-Fang; Yeh, Po-Chen; Chung, Tien-Kan
2017-01-01
In this paper, we demonstrate a miniature magnetic-force-based, three-axis, AC magnetic sensor with piezoelectric/vibrational energy-harvesting functions. For magnetic sensing, the sensor employs a magnetic–mechanical–piezoelectric configuration (which uses magnetic force and torque, a compact, single, mechanical mechanism, and the piezoelectric effect) to convert x-axis and y-axis in-plane and z-axis magnetic fields into piezoelectric voltage outputs. Under the x-axis magnetic field (sine-wave, 100 Hz, 0.2–3.2 gauss) and the z-axis magnetic field (sine-wave, 142 Hz, 0.2–3.2 gauss), the voltage output with the sensitivity of the sensor are 1.13–26.15 mV with 8.79 mV/gauss and 1.31–8.92 mV with 2.63 mV/gauss, respectively. In addition, through this configuration, the sensor can harness ambient vibrational energy, i.e., possessing piezoelectric/vibrational energy-harvesting functions. Under x-axis vibration (sine-wave, 100 Hz, 3.5 g) and z-axis vibration (sine-wave, 142 Hz, 3.8 g), the root-mean-square voltage output with power output of the sensor is 439 mV with 0.333 μW and 138 mV with 0.051 μW, respectively. These results show that the sensor, using this configuration, successfully achieves three-axis magnetic field sensing and three-axis vibration energy-harvesting. Due to these features, the three-axis AC magnetic sensor could be an important design reference in order to develop future three-axis AC magnetic sensors, which possess energy-harvesting functions, for practical industrial applications, such as intelligent vehicle/traffic monitoring, processes monitoring, security systems, and so on. PMID:28208693
Du, Zhongzhou; Su, Rijian; Liu, Wenzhong; Huang, Zhixing
2015-01-01
The signal transmission module of a magnetic nanoparticle thermometer (MNPT) was established in this study to analyze the error sources introduced during the signal flow in the hardware system. The underlying error sources that significantly affected the precision of the MNPT were determined through mathematical modeling and simulation. A transfer module path with the minimum error in the hardware system was then proposed through the analysis of the variations of the system error caused by the significant error sources when the signal flew through the signal transmission module. In addition, a system parameter, named the signal-to-AC bias ratio (i.e., the ratio between the signal and AC bias), was identified as a direct determinant of the precision of the measured temperature. The temperature error was below 0.1 K when the signal-to-AC bias ratio was higher than 80 dB, and other system errors were not considered. The temperature error was below 0.1 K in the experiments with a commercial magnetic fluid (Sample SOR-10, Ocean Nanotechnology, Springdale, AR, USA) when the hardware system of the MNPT was designed with the aforementioned method. PMID:25875188
Design of PCB search coils for AC magnetic flux density measurement
NASA Astrophysics Data System (ADS)
Ulvr, Michal
2018-04-01
This paper presents single-layer, double-layer and ten-layer planar square search coils designed for AC magnetic flux density amplitude measurement up to 1 T in the low frequency range in a 10 mm air gap. The printed-circuit-board (PCB) method was used for producing the search coils. Special attention is given to a full characterization of the PCB search coils including a comparison between the detailed analytical design method and the finite integration technique method (FIT) on the one hand, and experimental results on the other. The results show very good agreement in the resistance, inductance and search coil constant values (the area turns) and also in the frequency dependence of the search coil constant.
Rapid magnetic microfluidic mixer utilizing AC electromagnetic field.
Wen, Chih-Yung; Yeh, Cheng-Peng; Tsai, Chien-Hsiung; Fu, Lung-Ming
2009-12-01
This paper presents a novel simple micromixer based on stable water suspensions of magnetic nanoparticles (i.e. ferrofluids). The micromixer chip is built using standard microfabrication and simple soft lithography, and the design can be incorporated as a subsystem into any chemical microreactor or a miniaturized biological sensor. An electromagnet driven by an AC power source is used to induce transient interactive flows between a ferrofluid and Rhodamine B. The alternative magnetic field causes the ferrofluid to expand significantly and uniformly toward Rhodamine B, associated with a great number of extremely fine fingering structures on the interface in the upstream and downstream regions of the microchannel. These pronounced fingering patterns, which have not been observed by other active mixing methods utilizing only magnetic force, increase the mixing interfacial length dramatically. Along with the dominant diffusion effects occurring around the circumferential regions of the fine finger structures, the mixing efficiency increases significantly. The miscible fingering instabilities are observed and applied in the microfluidics for the first time. This work is carried with a view to developing functionalized ferrofluids that can be used as sensitive pathogen detectors and the present experimental results demonstrate that the proposed micromixer has excellent mixing capabilities. The mixing efficiency can be as high as 95% within 2.0 s and a distance of 3.0 mm from the inlet of the mixing channel, when the applied peak magnetic field is higher than 29.2 Oe and frequency ranges from 45 to 300 Hz.
The effect of surface grain reversal on the AC losses of sintered Nd-Fe-B permanent magnets
NASA Astrophysics Data System (ADS)
Moore, Martina; Roth, Stefan; Gebert, Annett; Schultz, Ludwig; Gutfleisch, Oliver
2015-02-01
Sintered Nd-Fe-B magnets are exposed to AC magnetic fields in many applications, e.g. in permanent magnet electric motors. We have measured the AC losses of sintered Nd-Fe-B magnets in a closed circuit arrangement using AC fields with root mean square-values up to 80 mT (peak amplitude 113 mT) over the frequency range 50 to 1000 Hz. Two magnet grades with different dysprosium content were investigated. Around the remanence point the low grade material (1.7 wt% Dy) showed significant hysteresis losses; whereas the losses in the high grade material (8.9 wt% Dy) were dominated by classical eddy currents. Kerr microscopy images revealed that the hysteresis losses measured for the low grade magnet can be mainly ascribed to grains at the sample surface with multiple domains. This was further confirmed when the high grade material was subsequently exposed to DC and AC magnetic fields. Here a larger number of surface grains with multiple domains are also present once the step in the demagnetization curve attributed to the surface grain reversal is reached and a rise in the measured hysteresis losses is evident. If in the low grade material the operating point is slightly offset from the remanence point, such that zero field is not bypassed, its AC losses can also be fairly well described with classical eddy current theory.
Nikolo, Martin; Zapf, Vivien S.; Singleton, John; ...
2016-07-22
Vortex dynamics and nonlinear ac response are studied in a Ba(Fe 0.94Ni 0.06) 2As 2( T c= 18.5 K) bulk superconductor in magnetic fields up to 12 T via ac susceptibility measurements of the first ten harmonics. A comprehensive study of the ac magnetic susceptibility and its first ten harmonics finds shifts to higher temperatures with increasing ac measurement frequencies (10 to 10,000 Hz) for a wide range of ac (1, 5, and 10 Oe) and dc fields (0 to 12 T). The characteristic measurement time constant t1 is extracted from the exponential fit of the data and linked tomore » vortex relaxation. The Anderson-Kim Arrhenius law is applied to determine flux activation energy E a/k as a function dc magnetic field. The de-pinning, or irreversibility lines, were determined by a variety of methods and extensively mapped. The ac response shows surprisingly weak higher harmonic components, suggesting weak nonlinear behavior. Lastly, our data does not support the Fisher model; we do not see an abrupt vortex glass to vortex liquid transition and the resistivity does not drop to zero, although it appears to approach zero exponentially.« less
NASA Astrophysics Data System (ADS)
Kajikawa, Kazuhiro; Funaki, Kazuo
2011-12-01
Application of an external AC magnetic field parallel to superconducting tapes helps in eliminating the magnetization caused by the shielding current induced in the flat faces of the tapes. This method helps in realizing a magnet system with high-temperature superconducting tapes for magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) applications. The effectiveness of the proposed method is validated by numerical calculations carried out using the finite-element method and experiments performed using a commercially available superconducting tape. The field uniformity for a single-layer solenoid coil after the application of an AC field is also estimated by a theoretical consideration.
Corá, Luciana A; Romeiro, Fernando G; Paixão, Fabiano C; Américo, Madileine F; Oliveira, Ricardo B; Baffa, Oswaldo; Miranda, José Ricardo A
2006-08-01
To employ the AC Biosusceptometry (ACB) technique to evaluate in vitro and in vivo characteristics of enteric coated magnetic hydroxypropyl methylcellulose (HPMC) capsules and to image the disintegration process. HPMC capsules filled with ferrite (MnFe2O4) and coated with Eudragit were evaluated using USP XXII method and administered to fasted volunteers. Single and multisensor ACB systems were used to characterize the gastrointestinal (GI) motility and to determine gastric residence time (GRT), small intestinal transit time (SITT) and orocaecal transit time (OCTT). Mean disintegration time (t50) was quantified from 50% increase of pixels in the imaging area. In vitro and in vivo performance of the magnetic HPMC capsules as well as the disintegration process were monitored using ACB systems. The mean disintegration time (t50) calculated for in vitro was 25+/-5 min and for in vivo was 13+/-5 min. In vivo also were determined mean values for GRT (55+/-19 min), SITT (185+/-82 min) and OCTT (240+/-88 min). AC Biosusceptometry is a non-invasive technique originally proposed to monitoring pharmaceutical dosage forms orally administered and to image the disintegration process.
Magnetic force microscopy method and apparatus to detect and image currents in integrated circuits
Campbell, Ann. N.; Anderson, Richard E.; Cole, Jr., Edward I.
1995-01-01
A magnetic force microscopy method and improved magnetic tip for detecting and quantifying internal magnetic fields resulting from current of integrated circuits. Detection of the current is used for failure analysis, design verification, and model validation. The interaction of the current on the integrated chip with a magnetic field can be detected using a cantilevered magnetic tip. Enhanced sensitivity for both ac and dc current and voltage detection is achieved with voltage by an ac coupling or a heterodyne technique. The techniques can be used to extract information from analog circuits.
Magnetic force microscopy method and apparatus to detect and image currents in integrated circuits
Campbell, A.N.; Anderson, R.E.; Cole, E.I. Jr.
1995-11-07
A magnetic force microscopy method and improved magnetic tip for detecting and quantifying internal magnetic fields resulting from current of integrated circuits are disclosed. Detection of the current is used for failure analysis, design verification, and model validation. The interaction of the current on the integrated chip with a magnetic field can be detected using a cantilevered magnetic tip. Enhanced sensitivity for both ac and dc current and voltage detection is achieved with voltage by an ac coupling or a heterodyne technique. The techniques can be used to extract information from analog circuits. 17 figs.
NASA Astrophysics Data System (ADS)
Bejhed, Rebecca S.; Strømme, Maria; Svedlindh, Peter; Ahlford, Annika; Strömberg, Mattias
2015-12-01
Magnetic biosensors are promising candidates for low-cost point-of-care biodiagnostic devices. For optimal efficiency it is crucial to minimize the time and complexity of the assay protocol including target recognition, amplification, labeling and read-out. In this work, possibilities for protocol simplifications for a DNA biodetection principle relying on hybridization of magnetic nanobeads to rolling circle amplification (RCA) products are investigated. The target DNA is recognized through a padlock ligation assay resulting in DNA circles serving as templates for the RCA process. It is found that beads can be present during amplification without noticeably interfering with the enzyme used for RCA (phi29 polymerase). As a result, the bead-coil hybridization can be performed immediately after amplification in a one-step manner at elevated temperature within a few minutes prior to read-out in an AC susceptometer setup, i.e. a combined protocol approach. Moreover, by recording the phase angle ξ = arctan(χ″/χ'), where χ and χ″ are the in-phase and out-of-phase components of the AC susceptibility, respectively, at one single frequency the total assay time for the optimized combined protocol would be no more than 1.5 hours, often a relevant time frame for diagnosis of cancer and infectious disease. Also, applying the phase angle method normalization of AC susceptibility data is not needed. These findings are useful for the development of point-of-care biodiagnostic devices relying on bead-coil binding and magnetic AC susceptometry.
Kaushik, Ajeet; Nikkhah-Moshaie, Roozbeh; Sinha, Raju; Bhardwaj, Vinay; Atluri, Venkata; Jayant, Rahul Dev; Yndart, Adriana; Kateb, Babak; Pala, Nezih; Nair, Madhavan
2017-04-04
In this research, we demonstrate cell uptake of magneto-electric nanoparticles (MENPs) through nanoelectroporation (NEP) using alternating current (ac)-magnetic field stimulation. Uptake of MENPs was confirmed using focused-ion-beam assisted transmission electron microscopy (FIB-TEM) and validated by a numerical simulation model. The NEP was performed in microglial (MG) brain cells, which are highly sensitive for neuro-viral infection and were selected as target for nano-neuro-therapeutics. When the ac-magnetic field optimized (60 Oe at 1 kHz), MENPs were taken up by MG cells without affecting cell health (viability > 92%). FIB-TEM analysis of porated MG cells confirmed the non-agglomerated distribution of MENPs inside the cell and no loss of their elemental and crystalline characteristics. The presented NEP method can be adopted as a part of future nanotherapeutics and nanoneurosurgery strategies where a high uptake of a nanomedicine is required for effective and timely treatment of brain diseases.
Kaushik, Ajeet; Nikkhah-Moshaie, Roozbeh; Sinha, Raju; Bhardwaj, Vinay; Atluri, Venkata; Jayant, Rahul Dev; Yndart, Adriana; Kateb, Babak; Pala, Nezih; Nair, Madhavan
2017-01-01
In this research, we demonstrate cell uptake of magneto-electric nanoparticles (MENPs) through nanoelectroporation (NEP) using alternating current (ac)-magnetic field stimulation. Uptake of MENPs was confirmed using focused-ion-beam assisted transmission electron microscopy (FIB-TEM) and validated by a numerical simulation model. The NEP was performed in microglial (MG) brain cells, which are highly sensitive for neuro-viral infection and were selected as target for nano-neuro-therapeutics. When the ac-magnetic field optimized (60 Oe at 1 kHz), MENPs were taken up by MG cells without affecting cell health (viability > 92%). FIB-TEM analysis of porated MG cells confirmed the non-agglomerated distribution of MENPs inside the cell and no loss of their elemental and crystalline characteristics. The presented NEP method can be adopted as a part of future nanotherapeutics and nanoneurosurgery strategies where a high uptake of a nanomedicine is required for effective and timely treatment of brain diseases. PMID:28374799
Sensor-less pseudo-sinusoidal drive for a permanent-magnet brushless ac motor
NASA Astrophysics Data System (ADS)
Liu, Li-Hsiang; Chern, Tzuen-Lih; Pan, Ping-Lung; Huang, Tsung-Mou; Tsay, Der-Min; Kuang, Jao-Hwa
2012-04-01
The precise rotor-position information is required for a permanent-magnet brushless ac motor (BLACM) drive. In the conventional sinusoidal drive method, either an encoder or a resolver is usually employed. For position sensor-less vector control schemes, the rotor flux estimation and torque components are obtained by complicated coordinate transformations. These computational intensive methods are susceptible to current distortions and parameter variations. To simplify the method complexity, this work presents a sensor-less pseudo-sinusoidal drive scheme with speed control for a three-phase BLACM. Based on the sinusoidal drive scheme, a floating period of each phase current is inserted for back electromotive force detection. The zero-crossing point is determined directly by the proposed scheme, and the rotor magnetic position and rotor speed can be estimated simultaneously. Several experiments for various active angle periods are undertaken. Furthermore, a current feedback control is included to minimize and compensate the torque fluctuation. The experimental results show that the proposed method has a competitive performance compared with the conventional drive manners for BLACM. The proposed scheme is straightforward, bringing the benefits of sensor-less drive and negating the need for coordinate transformations in the operating process.
Method of driving liquid flow at or near the free surface using magnetic microparticles
Snezhko, Oleksiy [Woodridge, IL; Aronson, Igor [Darien, IL; Kwok, Wai-Kwong [Evanston, IL; Belkin, Maxim V [Woodridge, IL
2011-10-11
The present invention provides a method of driving liquid flow at or near a free surface using self-assembled structures composed of magnetic particles subjected to an external AC magnetic field. A plurality of magnetic particles are supported at or near a free surface of liquid by surface tension or buoyancy force. An AC magnetic field traverses the free surface and dipole-dipole interaction between particles produces in self-assembled snake structures which oscillate at the frequency of the traverse AC magnetic field. The snake structures independently move across the free surface and may merge with other snake structures or break up and coalesce into additional snake structures experiencing independent movement across the liquid surface. During this process, the snake structures produce asymmetric flow vortices across substantially the entirety of the free surface, effectuating liquid flow across the free surface.
AC transport in p-Ge/GeSi quantum well in high magnetic fields
DOE Office of Scientific and Technical Information (OSTI.GOV)
Drichko, I. L.; Malysh, V. A.; Smirnov, I. Yu.
2014-08-20
The contactless surface acoustic wave technique is implemented to probe the high-frequency conductivity of a high-mobility p-Ge/GeSi quantum well structure in the regime of integer quantum Hall effect (IQHE) at temperatures 0.3–5.8 K and magnetic fields up to 18 T. It is shown that, in the IQHE regime at the minima of conductivity, holes are localized and ac conductivity is of hopping nature and can be described within the “two-site” model. The analysis of the temperature and magnetic-field-orientation dependence of the ac conductivity at odd filing factors enables us to determine the effective hole g-factor, |g{sub zz}|≈4.5. It is shownmore » that the in-plane component of the magnetic field leads to a decrease in the g-factor as well as increase in the cyclotron mass, which is explained by orbital effects in the complex valence band of germanium.« less
Hard permanent magnet development trends and their application to A.C. machines
NASA Technical Reports Server (NTRS)
Mildrum, H. F.
1981-01-01
The physical and magnetic properties of Mn-Al-C, Fe-Cr-Co, and RE-TM (rare earth-transition metal intermetallics) in polymer and soft metal bonded or sintered form are considered for ac circuit machine usage. The manufacturing processes for the magnetic materials are reviewed, and the mechanical and electrical properties of the magnetic materials are compared, with consideration given to the reference Alnico magnet. The Mn-Al-C magnets have the same magnetic properties and costs as Alnico units, operate well at low temperatures, but have poor high temperature performance. Fe-Cr-Co magnets also have comparable cost to Alnico magnets, and operate at high or low temperature, but are brittle, expensive, and contain Co. RE-Co magnets possess a high energy density, operate well in a wide temperature range, and are expensive. Recommendation for exploring the rare-earth alternatives are offered.
Measured losses in superconductor magnets for 60-Hertz ac operation.
NASA Technical Reports Server (NTRS)
Hamlet, I. L.; Kilgore, R. A.
1971-01-01
Results of an experimental study of electrical losses in superconductor magnets. Preliminary 60-Hz ac loss data are presented for coils constructed of Nb3Sn ribbon, Nb-Ti cable, and multifilament Nb-Ti. Losses have been measured for different size coils up to approximately 20 cm in diameter. Of the conductor types tested, Nb3Sn ribbon has the lowest losses for ac operation. In Nb3Sn-ribbon coils of different sizes, the loss per unit length of conductor is shown to decrease with a decrease in the rate of change of current and to increase, in general, with increase in coil size. An important aspect of the study is the high degree of repeatability of the data.
NASA Astrophysics Data System (ADS)
Ford, Kris; Mair, Lamar; Fisher, Mike; Rowshon Alam, Md.; Juliano, Rudolph; Superfine, Richard
2008-10-01
In order to make non-viral gene delivery a useful tool in the study and treatment of genetic disorders, it is imperative that these methodologies be further refined to yield optimal results. Transfection of magnetic nanoparticles and nanorods are used as non-viral gene vectors to transfect HeLa EGFP-654 cells that stably express a mutated enhanced green fluorescent protein (EGFP) gene. We deliver antisense oligonucleotides to these cells designed to correct the aberrant splicing caused by the mutation in the EGFP gene. We also transfect human bronchial endothelial cells and immortalized WI-38 lung cells with pEGFP-N1 vectors. To achieve this we bind the genes to magnetic nanoparticles and nanorods and introduce magnetic fields to effect transfection. We wish to examine the effects of magnetic fields on the transfection of these particles and the benefits of using alternating (AC) magnetic fields in improving transfection rates over direct (DC) magnetic fields. We specifically look at the frequency dependence of the AC field and particle aspect ratio as it pertains to influencing transfection rate. We posit that the increase in angular momentum brought about by the AC field and the high aspect ratio of the nanorod particles, is vital to generating the force needed to move the particle through the cell membrane.
Magnetic field tunable ac electrical transport of LaFeO3-wax nanocomposites
NASA Astrophysics Data System (ADS)
Roy, Supratim; Mandal, S. K.; Debnath, Rajesh; Nath, Debajyoti; Dey, P.
2018-04-01
Single phase perovskite LaFeO3 nanoparticles have been prepared through chemical pyrophoric reaction process. It is further grinded with paraffin wax of quantity 0.5 wt% of total composition to obtain an organic composite 99.5%LaFeO3-0.5%Wax. Studies of ac electrical properties viz. complex impedance, dielectric response, loss coefficient have been done in presence of external dc magnetic field, which reveals a good magnetoimpedance (˜221%) and a negative magnetodielectric (˜ 64%). The value of impedance, its real and imaginary part is observed to increase with dc field. The composite exhibits high dielectric constant (˜4760). The ac conductivity is found to decrease with applied field and increase with ac frequency.
Magnetic relaxation phenomena in the chiral magnet Fe1 -xCoxSi : An ac susceptibility study
NASA Astrophysics Data System (ADS)
Bannenberg, L. J.; Lefering, A. J. E.; Kakurai, K.; Onose, Y.; Endoh, Y.; Tokura, Y.; Pappas, C.
2016-10-01
We present a systematic study of the ac susceptibility of the chiral magnet Fe1 -xCoxSi with x =0.30 covering four orders of magnitude in frequencies from 0.1 Hz to 1 kHz, with particular emphasis to the pronounced history dependence. Characteristic relaxation times ranging from a few milliseconds to tens of seconds are observed around the skyrmion lattice A phase, the helical-to-conical transition and in a region above TC. The distribution of relaxation frequencies around the A phase is broad, asymmetric, and originates from multiple coexisting relaxation processes. The pronounced dependence of the magnetic phase diagram on the magnetic history and cooling rates as well as the asymmetric frequency dependence and slow dynamics suggest more complicated physical phenomena in Fe0.7Co0.3Si than in other chiral magnets.
NASA Astrophysics Data System (ADS)
Murphy, J. P.; Gheorghiu, N. N.; Bullard, T.; Haugan, T.; Sumption, M. D.; Majoros, M.; Collings, E. W.
2017-09-01
A new facility for the measurement of AC loss in superconductors at high dB/dt has been developed. The test device has a spinning rotor consisting of permanent magnets arranged in a Halbach array; the sample, positioned outside of this, is exposed to a time varying AC field with a peak radial field of 0.566 T. At a rotor speed of 3600 RPM the frequency of the AC field is 240 Hz, the radial dB/dt is 543 T/s and the tangential dB/dt is 249 T/s. Loss is measured using nitrogen boiloff from a double wall calorimeter feeding a gas flow meter. The system is calibrated using power from a known resistor. YBCO tape losses were measured in the new device and compared to the results from a solenoidal magnet AC loss system measurement of the same samples (in this latter case measurements were limited to a field of amplitude 0.1 T and a dB/dt of 100 T/s). Solenoidal magnet system AC loss measurements taken on a YBCO sample agreed with the Brandt loss expression associated with a 0-0.1 T Ic of 128 A. Subsequently, losses for two more YBCO tapes nominally identical to the first were individually measured in this spinning magnet calorimeter (SMC) machine with a Bmax of 0.566 T and dB/dt of up to 272 T/s. The losses, compared to a simplified version of the Brandt expression, were consistent with the average Ic expected for the tape in the 0-0.5 T range at 77 K. The eddy current contribution was consistent with a 77 K residual resistance ratio, RR, of 4.0. The SMC results for these samples agreed to within 5%. Good agreement was also obtained between the results of the SMC AC loss measurement and the solenoidal magnet AC loss measurement on the same samples.
NASA Astrophysics Data System (ADS)
Edwards, Rachel S.; Hill, Stephen; North, J. Micah; Dalal, Naresh; Jones, Shaela; Maccagnano, Sara
2003-03-01
We present high frequency high field electron paramagnetic resonance (EPR) measurements on the single molecule magnet Mn_12-Ac. Using a split coil magnet and highly sensitive resonant cavity techniques we are able to perform an angle dependent study of the single crystal EPR with the field applied in the hard plane, and hence unambiguously determine the transverse Hamiltonian parameters to fourth order. A variation in the line-shape of the resonances with angle supports the recent proposal of a ligand disorder in this material causing local quadratic anisotropy, and is used to determine the magnitude of the second order transverse term. This could have important implications for describing magnetic quantum tunneling in Mn_12-Ac. S. Hill, J.A.A.J. Perenboom, N.S. Dalal, T. Hathaway, T. Stalcup and J.S. Brooks, Phys. Rev. Lett. 80, 2453 (1998). A. Cornia, R. Sessoli, L. Sorace, D. Gatteschi, A.L. Barra and C. Daiguebonne, cond-mat/0112112.
NASA Astrophysics Data System (ADS)
Jang, Jung-tak; Bae, Seongtae
2017-10-01
The effects of Mg doping on the magnetic and AC self-heating temperature rising characteristics of γ-Fe2O3 superparamagnetic nanoparticles (SPNPs) were investigated for hyperthermia applications in biomedicine. The doping concentration of nonmagnetic Mg2+ cation was systematically controlled from 0 to 0.15 at. % in Mgx-γFe2O3 SPNPs during chemically and thermally modified one-pot thermal decomposition synthesis under bubbling O2/Ar gas mixture. It was empirically observed that the saturation magnetization (Ms) and the out-of-phase magnetic susceptibility ( χm″)of Mgx-γFe2O3 SPNPs were increased by increasing the Mg2+ cation doping concentration from 0.05 to 0.13 at. %. Correspondingly, the AC magnetically induced self-heating temperature (Tac,max) in solid state and the intrinsic loss power in water were increased up to 184 °C and 14.2 nH m2 kg-1 (Mgx-γFe2O3, x = 0.13), respectively, at the biologically and physiologically safe range of AC magnetic field (Happl × fappl = 1.2 × 109 A m-1 s-1). All the chemically and physically analyzed results confirmed that the dramatically improved AC magnetic induction heating characteristics and the magnetic properties of Mgx-γFe2O3 SPNPs (x = 0.13) are primarily due to the significantly enhanced magnetic susceptibility (particularly, χm″) and the improved AC/DC magnetic softness (lower AC/DC magnetic anisotropy) resulting from the systematically controlled nonmagnetic Mg2+ cation concentrations and distributions (occupation ratio) in the Fe vacancy sites of γ-Fe2O3 (approximately 12% vacancy), instead of typically well-known Fe3O4 (no vacancy) SPNPs. The cell viability and biocompatibility with U87 MG cell lines demonstrated that Mgx-γFe2O3 SPNPs (x = 0.13) has promising bio-feasibility for hyperthermia agent applications.
Effect of Dimension and Shape of Magnet on the Performance AC Generator with Translation Motion
NASA Astrophysics Data System (ADS)
Indriani, A.; Dimas, S.; Hendra
2018-02-01
The development of power plants using the renewable energy sources is very rapid. Renewable energy sources used solar energy, wind energy, ocean wave energy and other energy. All of these renewable energy sources require a processing device or a change of motion system to become electrical energy. One processing device is a generator which have work principle of converting motion (mechanical) energy into electrical energy with rotary shaft, blade and other motion components. Generator consists of several types of rotation motion and linear motion (translational). The generator have components such as rotor, stator and anchor. In the rotor and stator having magnet and winding coil as an electric generating part of the electric motion force. Working principle of AC generator with linear motion (translation) also apply the principle of Faraday that is using magnetic induction which change iron magnet to produce magnetic flux. Magnetic flux is captured by the stator to be converted into electrical energy. Linear motion generators consist of linear induction machine, wound synchronous machine field, and permanent magnet synchronous [1]. Performance of synchronous generator of translation motion is influenced by magnet type, magnetic shape, coil winding, magnetic and coil spacing and others. In this paper focus on the neodymium magnet with varying shapes, number of coil windings and gap of magnetic distances. This generator work by using pneumatic mechanism (PLTGL) for power plants system. Result testing of performance AC generator translation motion obtained that maximum voltage, current and power are 63 Volt for diameter winding coil 0.15 mm, number of winding coil 13000 and distance of magnet 20 mm. For effect shape of magnet, maximum voltage happen on rectangle magnet 30x20x5 mm with 4.64 Volt. Voltage and power on effect of diameter winding coil is 14.63 V and 17.82 W at the diameter winding coil 0.7 and number of winding coil is 1260 with the distance of magnet 25
Assay Methods for ACS Activity and ACS Phosphorylation by MAP Kinases In Vitro and In Vivo.
Han, Xiaomin; Li, Guojing; Zhang, Shuqun
2017-01-01
Ethylene, a gaseous phytohormone, has profound effects on plant growth, development, and adaptation to the environment. Ethylene-regulated processes begin with the induction of ethylene biosynthesis. There are two key steps in ethylene biosynthesis. The first is the biosynthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) from S-Adenosyl-Methionine (SAM), a common precursor in many metabolic pathways, which is catalyzed by ACC synthase (ACS). The second is the oxidative cleavage of ACC to form ethylene under the action of ACC oxidase (ACO). ACC biosynthesis is the committing and generally the rate-limiting step in ethylene biosynthesis. As a result, characterizing the cellular ACS activity and understanding its regulation are important. In this chapter, we detail the methods used to measure, (1) the enzymatic activity of both recombinant and native ACS proteins, and (2) the phosphorylation of ACS protein by mitogen-activated protein kinases (MAPKs) in vivo and in vitro.
Advanced AC permanent magnet axial flux disc motor for electric passenger vehicle
NASA Technical Reports Server (NTRS)
Kliman, G. B.
1982-01-01
An ac permanent magnet axial flux disc motor was developed to operate with a thyristor load commutated inverter as part of an electric vehicle drive system. The motor was required to deliver 29.8 kW (40 hp) peak and 10.4 kW (14 hp) average with a maximum speed of 11,000 rpm. It was also required to run at leading power factor to commutate the inverter. Three motors were built.
Hybrid immersed interface-immersed boundary methods for AC dielectrophoresis
DOE Office of Scientific and Technical Information (OSTI.GOV)
Hossan, Mohammad Robiul; Department of Engineering and Physics, University of Central Oklahoma, Edmond, OK 73034-5209; Dillon, Robert
2014-08-01
Dielectrophoresis, a nonlinear electrokinetic transport mechanism, has become popular in many engineering applications including manipulation, characterization and actuation of biomaterials, particles and biological cells. In this paper, we present a hybrid immersed interface–immersed boundary method to study AC dielectrophoresis where an algorithm is developed to solve the complex Poisson equation using a real variable formulation. An immersed interface method is employed to obtain the AC electric field in a fluid media with suspended particles and an immersed boundary method is used for the fluid equations and particle transport. The convergence of the proposed algorithm as well as validation of themore » hybrid scheme with experimental results is presented. In this paper, the Maxwell stress tensor is used to calculate the dielectrophoretic force acting on particles by considering the physical effect of particles in the computational domain. Thus, this study eliminates the approximations used in point dipole methods for calculating dielectrophoretic force. A comparative study between Maxwell stress tensor and point dipole methods for computing dielectrophoretic forces are presented. The hybrid method is used to investigate the physics of dielectrophoresis in microfluidic devices using an AC electric field. The numerical results show that with proper design and appropriate selection of applied potential and frequency, global electric field minima can be obtained to facilitate multiple particle trapping by exploiting the mechanism of negative dielectrophoresis. Our numerical results also show that electrically neutral particles form a chain parallel to the applied electric field irrespective of their initial orientation when an AC electric field is applied. This proposed hybrid numerical scheme will help to better understand dielectrophoresis and to design and optimize microfluidic devices.« less
NASA Astrophysics Data System (ADS)
Shen, Boyang; Li, Chao; Geng, Jianzhao; Zhang, Xiuchang; Gawith, James; Ma, Jun; Liu, Yingzhen; Grilli, Francesco; Coombs, T. A.
2018-07-01
This paper presents a comprehensive alternating current (AC) loss study of a circular high temperature superconductor (HTS) coated conductor coil. The AC losses from a circular double pancake coil were measured using the electrical method. A 2D axisymmetric H -formulation model using the FEM package in COMSOL Multiphysics has been established to match the circular geometry of the coil used in the experiment. Three scenarios have been analysed: Scenario 1 with AC transport current and DC magnetic field (experiment and simulation); Scenario 2 with DC transport current and AC magnetic field (simulation); and Scenario 3 with AC transport current and AC magnetic field (simulation and experimental data support). The angular dependence analysis on the coil under a magnetic field with different orientation angle θ has been carried out for all three scenarios. For Scenario 3, the effect of the relative phase difference Δφ between the AC current and the AC field on the total AC loss of the coil has been investigated. In summary, a current/field/angle/phase dependent AC loss ( I , B , θ, Δφ) study of a circular HTS coil has been carried out. The obtained results provide useful indications for the future design and research of HTS AC systems.
Study of the Dependence on Magnetic Field and Bias Voltage of an AC-Biased TES Microcalorimeter
NASA Technical Reports Server (NTRS)
Bandler, Simon
2011-01-01
At SRON we are studying the performance of a Goddard Space Flight Center single pixel TES microcalorimeter operated in the AC bias configuration. For x-ray photons at 6keV the AC biased pixel shows a best energy resolution of 3.7eV, which is about a factor of 2 worse than the energy resolution observed in identical DC-biased pixels. To better understand the reasons of this discrepancy, we investigated the detector performance as a function of temperature, bias working point and applied magnetic field. A strong periodic dependence of the detector noise on the TES AC bias voltage is measured. We discuss the results in the framework of the recent weak-link behaviour observed inTES microcalorimeters.
Bogren, Sara; Fornara, Andrea; Ludwig, Frank; del Puerto Morales, Maria; Steinhoff, Uwe; Fougt Hansen, Mikkel; Kazakova, Olga; Johansson, Christer
2015-01-01
This study presents classification of different magnetic single- and multi-core particle systems using their measured dynamic magnetic properties together with their nanocrystal and particle sizes. The dynamic magnetic properties are measured with AC (dynamical) susceptometry and magnetorelaxometry and the size parameters are determined from electron microscopy and dynamic light scattering. Using these methods, we also show that the nanocrystal size and particle morphology determines the dynamic magnetic properties for both single- and multi-core particles. The presented results are obtained from the four year EU NMP FP7 project, NanoMag, which is focused on standardization of analysis methods for magnetic nanoparticles. PMID:26343639
Generating an AC amplitude magnetic flux density value up to 150 μT at a frequency up to 100 kHz
NASA Astrophysics Data System (ADS)
Ulvr, Michal; Polonský, Jakub
2017-05-01
AC magnetic field analyzers with a triaxial coil probe are widely used by health and safety professionals, in manufacturing, and in service industries. For traceable calibration of these analyzers, it is important to be able to generate a stable, homogeneous reference AC magnetic flux density (MFD). In this paper, the generating of AC amplitude MFD value of 150 μT by single-layer Helmholtz type solenoid, described in previous work, was expanded up to a frequency of 100 kHz using the effect of serial resonance. A programmable capacitor array has been developed with a range of adjustable values from 50 pF to 51225 pF. In addition, the multi-layer search coil with a nominal area turns value of 1.3m2, used for adjusting AC MFD in the solenoid, has been modified by a transimpedance amplifier for use in a wider frequency range than up to 3 kHz. The possibility of using the programmable capacitor array up to 150 kHz has also been tested. An AC amplitude MFD value of 150 μT can be generated with expanded uncertainty better than 0.6% up to 100 kHz.
System and method for determining stator winding resistance in an AC motor
Lu, Bin [Kenosha, WI; Habetler, Thomas G [Snellville, GA; Zhang, Pinjia [Atlanta, GA; Theisen, Peter J [West Bend, WI
2011-05-31
A system and method for determining stator winding resistance in an AC motor is disclosed. The system includes a circuit having an input connectable to an AC source and an output connectable to an input terminal of an AC motor. The circuit includes at least one contactor and at least one switch to control current flow and terminal voltages in the AC motor. The system also includes a controller connected to the circuit and configured to modify a switching time of the at least one switch to create a DC component in an output of the system corresponding to an input to the AC motor and determine a stator winding resistance of the AC motor based on the injected DC component of the voltage and current.
The application of Halbach cylinders to brushless ac servo motors
DOE Office of Scientific and Technical Information (OSTI.GOV)
Atallah, K.; Howe, D.
1998-07-01
Halbach cylinders are applied to brushless ac servo motors. It is shown that a sinusoidal back-emf waveform and a low cogging torque can be achieved without recourse to conventional design features such as distributed windings and/or stator/rotor skew. A technique for imparting a multipole Halbach magnetization distribution on an isotropic permanent magnet cylinder is described, and it is shown that the torque capability of a Halbach ac servo motor can be up to 33% higher than conventional brushless permanent magnet ac motors.
NASA Astrophysics Data System (ADS)
Heydari, Hossein; Faghihi, Faramarz; Aligholizadeh, Reza
2008-01-01
AC loss is one of the important parameters in HTS (high temperature superconducting) AC devices. Among the HTS AC power devices, the transformer is an essential part in the electrical power system. The AC losses in an HTS tape depend on the magnetic field. One of the techniques usually adopted to mitigate the unwanted magnetic field is using a system of coils that produce a magnetic field opposite to the incident one, reducing the total magnetic field. In this paper adding two auxiliary windings to the HTS transformer to produce this opposite magnetic field is proposed. The proper use of these auxiliary windings could reduce the leakage flux and, therefore, the AC loss. A mathematical model is used to describe the behaviour of a transformer operating with auxiliary windings, based on the theory of electromagnetic coupled circuits. The influence of the auxiliary windings on the leakage field is studied by the finite element method (FEM) and the AC loss of an HTS transformer was calculated. Also, the simulation results show that employing auxiliary windings will improve the HTS transformer efficiency.
Rachakatla, Raja Shekar; Balivada, Sivasai; Seo, Gwi-Moon; Myers, Carl B; Wang, Hongwang; Samarakoon, Thilani N.; Dani, Raj; Pyle, Marla; Kroh, Franklin O.; Walker, Brandon; Leaym, Xiaoxuan; Koper, Olga B.; Chikan, Viktor; Bossmann, Stefan H.; Tamura, Masaaki; Troyer, Deryl L.
2010-01-01
Localized magnetic hyperthermia as a treatment modality for cancer has generated renewed interest, particularly if it can be targeted to the tumor site. We examined whether tumor-tropic neural progenitor cells (NPCs) could be utilized as cell delivery vehicles for achieving preferential accumulation of core/shell iron/iron oxide magnetic nanoparticles (MNPs) within a mouse model of melanoma. We developed aminosiloxane-porphyrin functionalized MNPs, evaluated cell viability and loading efficiency, and transplanted neural progenitor cells loaded with this cargo into mice with melanoma. NPCs were efficiently loaded with core/shell Fe/Fe3O4 MNPs with minimal cytotoxicity; the MNPs accumulated as aggregates in the cytosol. The NPCs loaded with MNPs could travel to subcutaneous melanomas, and after A/C (alternating current) magnetic field (AMF) exposure, the targeted delivery of MNPs by the cells resulted in a measurable regression of the tumors. The tumor attenuation was significant (p<0.05) a short time (24 hours) after the last of three AMF exposures. PMID:21058696
Optimization of spin-torque switching using AC and DC pulses
DOE Office of Scientific and Technical Information (OSTI.GOV)
Dunn, Tom; Kamenev, Alex; Fine Theoretical Physics Institute, University of Minnesota, Minneapolis, Minnesota 55455
2014-06-21
We explore spin-torque induced magnetic reversal in magnetic tunnel junctions using combined AC and DC spin-current pulses. We calculate the optimal pulse times and current strengths for both AC and DC pulses as well as the optimal AC signal frequency, needed to minimize the Joule heat lost during the switching process. The results of this optimization are compared against numeric simulations. Finally, we show how this optimization leads to different dynamic regimes, where switching is optimized by either a purely AC or DC spin-current, or a combination AC/DC spin-current, depending on the anisotropy energies and the spin-current polarization.
Snezhko, Oleksiy [Woodridge, IL; Aronson, Igor [Darien, IL; Kwok, Wai-Kwong [Downers Grove, IL
2011-01-25
Self-assembly of magnetic microparticles in AC magnetic fields. Excitation of the system by an AC magnetic field provides a variety of patterns that can be controlled by adjusting the frequency and the amplitude of the field. At low particle densities the low-frequency magnetic excitation favors cluster phase formation, while high frequency excitation favors chains and netlike structures. For denser configurations, an abrupt transition to the network phase was obtained.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Gung, C.Y.
1993-01-01
Energy dissipation, which is also called AC loss, of a composite multifilamentary superconducting wire is one of the most fundamental concerns in building a stable superconducting magnet. Characterization and reduction of AC losses are especially important in designing a superconducting magnet for generating transient magnetic fields. The goal of this thesis is to improve the understanding of AC-loss properties of superconducting wires developed for high-current ramp-field magnet applications. The major tasks include: (1) building an advanced AC-loss measurement system, (2) measuring AC losses of superconducting wires under simulated pulse magnet operations, (3) developing an analytical model for explaining the newmore » AC-loss properties found in the experiment, and (4) developing a computational methodology for comparing AC losses of a superconducting wire with those of a cable for a superconducting pulse magnet. A new experimental system using an isothermal calorimetric method was designed and constructed to measure the absolute AC losses in a composite superconductor. This unique experimental setup is capable of measuring AC losses of a brittle Nb{sub 3}Sn wire carrying high AC current in-phase with a large-amplitude pulse magnetic field. Improvements of the accuracy and the efficiency of this method are discussed. Three different types of composite wire have been measured: a Nb{sub 3}Sn modified jelly-roll (MJR) internal-tin wire used in a prototype ohmic heating coil, a Nb{sub 3}Sn internal-tin wire developed for a fusion reactor ohmic heating coil, and a NbTi wire developed for the magnets in a particle accelerator. The cross sectional constructions of these wires represent typical commercial wires manufactured for pulse magnet applications.« less
NASA Astrophysics Data System (ADS)
Šouc, J.; Vojenčiak, M.; Gömöry, F.
2010-04-01
Several short cable models were constructed from YBCO coated conductor (YBCO CC) to study their basic dc and ac electrical properties. They were prepared using superconducting tapes helically wound on fiberglass former of different diameter (5, 8 and 10 mm) with different twist pitch (from 1.7 up to 2.4 cm). The number of parallel-connected tapes ranged from 1 up to 6. The standard length of the models was 11 cm. In one case a 35 cm long model has been manufactured in order to perform a bending test. We observed that the critical currents of the models were proportional to the number of tapes used for their construction. Transport and magnetization ac loss were measured at 36 and 72 Hz.
Study of the Dependency on Magnetic Field and Bias Voltage of an AC-Biased TES Microcalorimeter
NASA Technical Reports Server (NTRS)
Gottardi, L.; Bruijn, M.; denHartog, R.; Hoevers, H.; deKorte, P.; vanderKuur, J.; Linderman, M.; Adams, J.; Bailey, C.; Bandler, S.;
2012-01-01
At SRON we are studying the performance of a Goddard Space Flight Center single pixel TES microcalorimeter operated in an AC bias configuration. For x-ray photons at 6 keV the pixel shows an x-ray energy resolution Delta E(sub FWHM) = 3.7 eV, which is about a factor 2 worse than the energy resolution observed in an identical DC-biased pixel. In order to better understand the reasons for this discrepancy we characterized the detector as a function of temperature, bias working point and applied perpendicular magnetic field. A strong periodic dependency of the detector noise on the TES AC bias voltage is measured. We discuss the results in the framework of the recently observed weak-link behaviour of a TES microcalorimeter.
Dynamic model tracking design for low inertia, high speed permanent magnet ac motors.
Stewart, P; Kadirkamanathan, V
2004-01-01
Permanent magnet ac (PMAC) motors have existed in various configurations for many years. The advent of rare-earth magnets and their associated highly elevated levels of magnetic flux makes the permanent magnet motor attractive for many high performance applications from computer disk drives to all electric racing cars. The use of batteries as a prime storage element carries a cost penalty in terms of the unladen weight of the vehicle. Minimizing this cost function requires the minimum electric motor size and weight to be specified, while still retaining acceptable levels of output torque. This tradeoff can be achieved by applying a technique known as flux weakening which will be investigated in this paper. The technique allows the speed range of a PMAC motor to be greatly increased, giving a constant power range of more than 4:1. A dynamic model reference controller is presented which has advantages in ease of implementation, and is particularly suited to dynamic low inertia applications such as clutchless gear changing in high performance electric vehicles. The benefits of this approach are to maximize the torque speed envelope of the motor, particularly advantageous when considering low inertia operation. The controller is examined experimentally, confirming the predicted performance.
Nonlinear AC susceptibility, surface and bulk shielding
NASA Astrophysics Data System (ADS)
van der Beek, C. J.; Indenbom, M. V.; D'Anna, G.; Benoit, W.
1996-02-01
We calculate the nonlinear AC response of a thin superconducting strip in perpendicular field, shielded by an edge current due to the geometrical barrier. A comparison with the results for infinite samples in parallel field, screened by a surface barrier, and with those for screening by a bulk current in the critical state, shows that the AC response due to a barrier has general features that are independent of geometry, and that are significantly different from those for screening by a bulk current in the critical state. By consequence, the nonlinear (global) AC susceptibility can be used to determine the origin of magnetic irreversibility. A comparison with experiments on a Bi 2Sr 2CaCu 2O 8+δ crystal shows that in this material, the low-frequency AC screening at high temperature is mainly due to the screening by an edge current, and that this is the unique source of the nonlinear magnetic response at temperatures above 40 K.
NASA Technical Reports Server (NTRS)
Noever, David A.; Koczor, Ronald J.; Roberson, Rick
1998-01-01
We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of large bulk-processed high-temperature superconductors. Podkietnov, et al (Podkietnov, E. and Nieminen, R. (1992) A Possibility of Gravitational Force Shielding by Bulk YBa2 Cu3 O7-x Superconductor, Physica C, C203:441-444.) have indicated that rotating AC fields play an essential role in their observed distortion of combined gravity and barometric pressure readings. We report experiments on large (15 cm diameter) bulk YBCO ceramic superconductors placed in the core of a three-phase, AC motor stator. The applied rotating field produces up to a 12,000 revolutions per minute magnetic field. The field intensity decays rapidly from the maximum at the outer diameter of the superconducting disk (less than 60 Gauss) to the center (less than 10 Gauss). This configuration was applied with and without a permanent DC magnetic field levitating the superconducting disk, with corresponding gravity readings indicating an apparent increase in observed gravity of less than 1 x 10(exp -6)/sq cm, measured above the superconductor. No effect of the rotating magnetic field or thermal environment on the gravimeter readings or on rotating the superconducting disk was noted within the high precision of the observation. Implications for propulsion initiatives and power storage flywheel technologies for high temperature superconductors will be discussed for various spacecraft and satellite applications.
Self-induced pinning of vortices in the presence of ac driving force in magnetic superconductors
NASA Astrophysics Data System (ADS)
Bulaevskii, Lev N.; Lin, Shi-Zeng
2012-12-01
We derive the response of the magnetic superconductors in the vortex state to the ac Lorentz force, FL(t)=Facsin(ωt), taking into account the interaction of vortices with the magnetic moments described by the relaxation dynamics (polaronic effect). At low amplitudes of the driving force Fac the dissipation in the system is suppressed due to the enhancement of the effective viscosity at low frequencies and due to formation of the magnetic pinning at high frequencies ω. In the adiabatic limit with low frequencies ω and high amplitude of the driving force Fac, the vortex and magnetic polarization form a vortex polaron when FL(t) is small. When FL increases, the vortex polaron accelerates and at a threshold driving force, the vortex polaron dissociates and the motion of vortex and the relaxation of magnetization are decoupled. When FL decreases, the vortex is retrapped by the background of remnant magnetization and they again form vortex polaron. This process repeats when FL(t) increases in the opposite direction. Remarkably, after dissociation, decoupled vortices move in the periodic potential induced by magnetization which remains for some periods of time due to retardation after the decoupling. At this stage vortices oscillate with high frequencies determined by the Lorentz force at the moment of dissociation. We derive also the creep rate of vortices and show that magnetic moments suppress creep rate.
Study of the Dependency on Magnetic Field and Bias Voltage of an AC-Biased TES Microcalorimeter.
Gottardi, L; Adams, J; Bailey, C; Bandler, S; Bruijn, M; Chervenak, J; Eckart, M; Finkbeiner, F; den Hartog, R; Hoevers, H; Kelley, R; Kilbourne, C; de Korte, P; van der Kuur, J; Lindeman, M; Porter, F; Sadlier, J; Smith, S
At SRON we are studying the performance of a Goddard Space Flight Center single pixel TES microcalorimeter operated in an AC bias configuration. For x-ray photons at 6 keV the pixel shows an x-ray energy resolution Δ E FWHM =3.7 eV, which is about a factor 2 worse than the energy resolution observed in an identical DC-biased pixel. In order to better understand the reasons for this discrepancy we characterised the detector as a function of temperature, bias working point and applied perpendicular magnetic field. A strong periodic dependency of the detector noise on the TES AC bias voltage is measured. We discuss the results in the framework of the recently observed weak-link behaviour of a TES microcalorimeter.
Diagnostics of the Fermilab Tevatron using an AC dipole
DOE Office of Scientific and Technical Information (OSTI.GOV)
Miyamoto, Ryoichi
2008-08-01
The Fermilab Tevatron is currently the world's highest energy colliding beam facility. Its counter-rotating proton and antiproton beams collide at 2 TeV center-of-mass. Delivery of such intense beam fluxes to experiments has required improved knowledge of the Tevatron's beam optical lattice. An oscillating dipole magnet, referred to as an AC dipole, is one of such a tool to non-destructively assess the optical properties of the synchrotron. We discusses development of an AC dipole system for the Tevatron, a fast-oscillating (f ~ 20 kHz) dipole magnet which can be adiabatically turned on and off to establish sustained coherent oscillations of themore » beam particles without affecting the transverse emittance. By utilizing an existing magnet and a higher power audio amplifier, the cost of the Tevatron AC dipole system became relatively inexpensive. We discuss corrections which must be applied to the driven oscillation measurements to obtain the proper interpretation of beam optical parameters from AC dipole studies. After successful operations of the Tevatron AC dipole system, AC dipole systems, similar to that in the Tevatron, will be build for the CERN LHC. We present several measurements of linear optical parameters (beta function and phase advance) for the Tevatron, as well as studies of non-linear perturbations from sextupole and octupole elements.« less
A MEMS sensor for AC electric current
NASA Astrophysics Data System (ADS)
Leland, Eli Sidney
This manuscript describes the development of a new MEMS sensor for the measurement of AC electric current. The sensor is comprised of a MEMS piezoelectric cantilever with a microscale permanent magnet mounted to the cantilever's free end. When placed near a wire carrying AC current, the magnet couples to the oscillating magnetic field surrounding the wire, causing the cantilever to deflect, and piezoelectric coupling produces a sinusoidal voltage proportional to the current in the wire. The sensor is itself passive, requiring no power supply to operate. It also operates on proximity and need only be placed near a current carrier in order to function. The sensor does not need to encircle the current carrier and it therefore can measure current in two-wire zip-cords without necessitating the separation of the two conductors. Applications for tins sensor include measuring residential and commercial electricity use and monitoring electric power distribution networks. An analytical model describing the behavior of the current sensor was developed. This model was also adapted to describe the power output of an energy scavenger coupled to a wire carrying AC current. A mesoscale sensor exhibited a sensitivity of 75 mV/A when measuring AC electric current in a zip-cord. A mesoscale energy scavenger produced 345 muW when coupled to a zip-cord carrying 13 A. MEMS current sensors were fabricated from aluminum nitride piezoelectric cantilevers and composite permanent magnets. The cantilevers were fabricated using a four-mask process. Microscale permanent magnets were dispenser-printed using NdFeB magnetic powder with an epoxy binder. The MEMS AC current sensor was interfaced with amplification circuitry and packaged inside an almninum enclosure. The sensor was also integrated with a mesoscale energy scavenger and power conditioning circuitry to create a fully self-powered current sensor. Unamplified sensitivity of the sensor was 0.1-1.1 mV/A when measuring currents in single
Magnetic helicity balance at Taylor relaxed states sustained by AC helicity injection
NASA Astrophysics Data System (ADS)
Hirota, Makoto; Morrison, Philip J.; Horton, Wendell; Hattori, Yuji
2017-10-01
Magnitudes of Taylor relaxed states that are sustained by AC magnetic helicity injection (also known as oscillating field current drive, OFCD) are investigated numerically in a cylindrical geometry. Compared with the amplitude of the oscillating magnetic field at the skin layer (which is normalized to 1), the strength of the axial guide field Bz 0 is shown to be an important parameter. The relaxation process seems to be active only when Bz 0 < 1 . Moreover, in the case of weak guide field Bz 0 < 0.2 , a helically-symmetric relaxed state is self-generated instead of the axisymmetric reversed-field pinch. As a theoretical model, the helicity balance is considered in a similar way to R. G. O'Neill et al., where the helicity injection rate is directly equated with the dissipation rate at the Taylor states. Then, the bifurcation to the helical Taylor state is predicted theoretically and the estimated magnitudes of the relaxed states reasonably agree with numerical results as far as Bz 0 < 1 . This work was supported by JSPS KAKENHI Grant Number 16K05627.
System and method for determining stator winding resistance in an AC motor using motor drives
Lu, Bin; Habetler, Thomas G; Zhang, Pinjia
2013-02-26
A system and method for determining the stator winding resistance of AC motors is provided. The system includes an AC motor drive having an input connectable to an AC source and an output connectable to an input terminal of an AC motor, a pulse width modulation (PWM) converter having switches therein to control current flow and terminal voltages in the AC motor, and a control system connected to the PWM converter. The control system generates a command signal to cause the PWM converter to control an output of the AC motor drive corresponding to an input to the AC motor, selectively generates a modified command signal to cause the PWM converter to inject a DC signal into the output of the AC motor drive, and determines a stator winding resistance of the AC motor based on the DC signal of at least one of the voltage and current.
Mi, Chris; Li, Siqi
2017-01-31
A bidirectional AC-DC converter is presented with reduced passive component size and common mode electro-magnetic interference. The converter includes an improved input stage formed by two coupled differential inductors, two coupled common and differential inductors, one differential capacitor and two common mode capacitors. With this input structure, the volume, weight and cost of the input stage can be reduced greatly. Additionally, the input current ripple and common mode electro-magnetic interference can be greatly attenuated, so lower switching frequency can be adopted to achieve higher efficiency.
A novel synthesis method for TiO2 particles with magnetic Fe3O4 cores.
Dong, Qi; Zhang, Keqiang; An, Yi
2014-01-01
TiO2@(AC/Fe3O4) (AC is activated carbon) was prepared by using AC and Fe3O4 as joint support. The morphological features, crystal structure, and magnetism of the final product were characterized. The results indicate that TiO2 particles formed on the surface of AC and Fe3O4; the sizes of TiO2 and Fe3O4 were 0.5 and 0.7 μm respectively, and that of AC fell within a wide range. The highly crystalline cubic structures of the TiO2 particles was in accord with the standard X-ray diffractometry spectrum of magnetite and anatase. The maximum saturation magnetization of TiO2@(AC/Fe3O4) was 75 emu g(-1), which was enough to support magnetic recovery. The rate of methylene blue (MB) removal photocatalyzed by TiO2@(AC/Fe3O4) was higher by 50% than that achieved with AC/Fe3O4 photocatalysis, and similar to that achieved with TiO2@AC. The removal rate (kobs) decreased drastically from 1.77 × 10(-2) to 9.36 × 10(-3)min(-1) when the initial concentration of MB solution increased from 2.0 to 5.0 mg L(-1). The kobs value increased from 9.41 × 10(-3) to 1.34 × 10(-2)min(-1) with increasing photocatalyst dosage from 0.2 to 1.0 g, then slightly decreased to 1.33 × 10(-2)min(-1) at 2.0 g dosage.
External Magnetic Field Reduction Techniques for the Advanced Stirling Radioisotope Generator
NASA Technical Reports Server (NTRS)
Niedra, Janis M.; Geng, Steven M.
2013-01-01
Linear alternators coupled to high efficiency Stirling engines are strong candidates for thermal-to-electric power conversion in space. However, the magnetic field emissions, both AC and DC, of these permanent magnet excited alternators can interfere with sensitive instrumentation onboard a spacecraft. Effective methods to mitigate the AC and DC electromagnetic interference (EMI) from solenoidal type linear alternators (like that used in the Advanced Stirling Convertor) have been developed for potential use in the Advanced Stirling Radioisotope Generator. The methods developed avoid the complexity and extra mass inherent in data extraction from multiple sensors or the use of shielding. This paper discusses these methods, and also provides experimental data obtained during breadboard testing of both AC and DC external magnetic field devices.
Concentrations of MUC16 and MUC5AC using three tear collection methods
Nichols, Jason J.
2017-01-01
Purpose To determine the optimal tear collection method for analysis of ocular surface mucins MUC5AC and MUC16. Methods Fifteen subjects without ocular surface disease were recruited. Subjects presented for tear collection on three separate days for three different tear collection methods with the order of method randomized. Methods used to collect tears from right and left eyes included Schirmer’s strip, basal tear collection, and flush tear collection. All samples from the right eyes were individually analyzed for MUC5AC whereas the left eye samples were individually analyzed for MUC16. For each individual sample, 10 μg of protein were loaded per lane into a 1% (w/v) agarose gel and run in electrophoresis buffer for 2 h. After overnight capillary transfer, membranes were incubated with either MUC5AC antibody CLH2 or MUC16 antibody OC125 for western blot analysis. Blots were developed with enhanced chemiluminescence (ECL) and signals captured with the Odyssey Fc (LI-COR). The relative amounts of MUC5AC and MUC16 were quantified with densitometry using software and compared for statistically significant differences between tear collection methods using the Kruskal–Wallis test in SPSS 22 and GraphPad Prism 7.02. Dunn’s multiple comparisons test was used for pairwise post-hoc comparisons. Results Samples containing less than 10 μg of total protein were not used for analysis which left eight samples (out of 45) unusable. The calculated MUC5AC median signal intensities from Schirmer’s strip, basal tears, and flush tears were 2.86 (n = 15, the interquartile range [IQR] = 2.54–3.21), 1.65 (n = 14, IQR = 1.34–3.1), and 1.67 (n = 9, IQR = 1.42–1.72), respectively (H = 9.5, p = 0.009). Post-hoc pairwise comparisons showed a statistically significant difference between Schirmer’s strip and flush tears (p = 0.01). The calculated MUC16 median signal intensities from Schirmer’s strip, basal tears, and flush tears were 1.88 (n = 14, IQR = 1.43–2.61), 5
Magnetic transit-time flowmeter
Forster, George A.
1976-07-06
The flow rate of a conducting fluid in a stream is determined by disposing two permanent-magnet flowmeters in the stream, one downstream of the other. Flow of the conducting fluid causes the generation of both d-c and a-c electrical signals, the a-c comprising flow noise. Measurement of the time delay between similarities in the a-c signals by cross-correlation methods provides a measure of the rate of flow of the fluid.
Numerical study on AC loss reduction of stacked HTS tapes by optimal design of flux diverter
NASA Astrophysics Data System (ADS)
Liu, Guole; Zhang, Guomin; Jing, Liwei; Yu, Hui
2017-12-01
High temperature superconducting (HTS) coils are key parts of many AC applications, such as generators, superconducting magnetic energy storage and transformers. AC loss reduction in HTS coils is essential for the commercialization of these HTS devices. Magnetic material is generally used as the flux diverter in an effort to reduce the AC loss in HTS coils. To achieve the greatest reduction in the AC loss of the coils, the flux diverter should be made of a material with low loss and high saturated magnetic density, and the optimization of the geometric size and location of the flux diverter is required. In this paper, we chose Ni-alloy as the flux diverter, which can be processed into a specific shape and size. The influence of the shape and location of the flux diverter on the AC loss characteristics of stacked (RE)BCO tapes is investigated by use of a finite element method. Taking both the AC loss of the (RE)BCO coils and the ferromagnetic loss of the flux diverter into account, the optimal geometry of the flux diverter is obtained. It is found that when the applied current is at half the value of the critical current, the total loss of the HTS stack with the optimal flux diverter is only 18% of the original loss of the HTS stack without the flux diverter. Besides, the effect of the flux diverter on the critical current of the (RE)BCO stack is investigated.
NASA Astrophysics Data System (ADS)
McCune, Robert C.; Upadhyay, Vinod; Wang, Yar-Ming; Battocchi, Dante
The potential utility of AC-DC-AC electrochemical methods in comparative measures of corrosion-resisting coating system performance for magnesium alloys under consideration for the USAMP "Magnesium Front End Research and Development" project was previously shown in this forum [1]. Additional studies of this approach using statistically-designed experiments have been conducted with focus on alloy types, pretreatment, topcoat material and topcoat thickness as the variables. Additionally, sample coupons made for these designed experiments were also subjected to a typical automotive cyclic corrosion test cycle (SAE J2334) as well as ASTM B117 for comparison of relative performance. Results of these studies are presented along with advantages and limitations of the proposed methodology.
Mandal Goswami, Madhuri
2016-01-01
This paper reports on synthesis of hollow spheres of magnetite, guided by micelles and their application in drug release by the stimulus responsive technique. Here oleyelamine micelles are used as the core substance for the formation of magnetite nano hollow spheres (NHS). Diameter and shell thickness of NHS have been changed by changing concentration of the micelles. Mechanism of NHS formation has been established by investigating the aliquot collected at different time during the synthesis of NHS. It has been observed that oleyelamine as micelles play an important role to generate hollow-sphere particles of different diameter and thickness just by varying its amount. Structural analysis was done by XRD measurement and morphological measurements, SEM and TEM were performed to confirm the shape and size of the NHS. FTIR measurement support the formation of magnetite phase too. Frequency dependent AC magnetic measurements and AC magnetic field stimulated drug release event by these particles provide a direction of the promising application of these NHS for better cancer treatment in near future. Being hollow & porous in structure and magnetic in nature, such materials will also be useful in other applications such as in removal of toxic materials, magnetic separation etc. PMID:27796329
Ebrahimi Zarandi, Mohammad Javad; Sohrabi, Mahmoud Reza; Khosravi, Morteza; Mansouriieh, Nafiseh; Davallo, Mehran; Khosravan, Azita
2016-01-01
This study synthesized magnetic nanoparticles (Fe(3)O(4)) immobilized on activated carbon (AC) and used them as an effective adsorbent for Cu(II) removal from aqueous solution. The effect of three parameters, including the concentration of Cu(II), dosage of Fe(3)O(4)/AC magnetic nanocomposite and pH on the removal of Cu(II) using Fe(3)O(4)/AC nanocomposite were studied. In order to examine and describe the optimum condition for each of the mentioned parameters, Taguchi's optimization method was used in a batch system and L9 orthogonal array was used for the experimental design. The removal percentage (R%) of Cu(II) and uptake capacity (q) were transformed into an accurate signal-to-noise ratio (S/N) for a 'larger-the-better' response. Taguchi results, which were analyzed based on choosing the best run by examining the S/N, were statistically tested using analysis of variance; the tests showed that all the parameters' main effects were significant within a 95% confidence level. The best conditions for removal of Cu(II) were determined at pH of 7, nanocomposite dosage of 0.1 gL(-1) and initial Cu(II) concentration of 20 mg L(-1) at constant temperature of 25 °C. Generally, the results showed that the simple Taguchi's method is suitable to optimize the Cu(II) removal experiments.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Moradi, J., E-mail: j_moradi@yahoo.com; Ghazi, M.E.; Ehsani, M.H., E-mail: mhe_ehsani@yahoo.com
2014-07-01
Nanoparticles of La{sub 0.8}Sr{sub 0.2}MnO{sub 3} (LSMO) with different particle sizes are synthesized by a very fast, inexpensive, reproducible, and environmentally friendly method: the microwave irradiation of the corresponding mixture of nitrates. The structural and magnetic properties of the samples are investigated by the X-Ray diffraction (XRD), Fourier transform infra-red (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and magnetic (DC magnetization and AC susceptibility) measurements. The XRD study coupled with the Rietveld refinement show that all samples crystallize in a rhombohedral structure with the space group of R−3C. The FT-IR spectroscopy and FE-SEM images indicate formationmore » of the perovskite structure of LSMO. The DC magnetization measurements confirm the decrease in the particle size effects on the magnetic properties, e.g. reduction in the ferromagnetic (FM) moment and increase in the surface spin disorder. Magnetic dynamics of the samples studied by AC magnetic susceptibility shows that the magnetic behavior of the nanometer-sized samples is well-described by the Vogel-Fulcher and critical slowing down laws. Strong interaction between magnetic nanoparticles of LSMO was detected by fitting the experimental data with the mentioned models. - Graphical abstract: Temperature dependence of the magnetization M(T) was measured in the zero-field-cooling (ZFC) and field-cooling (FC) modes at the applied magnetic field of 100 Oe for the La{sub 0.8}Sr{sub 0.2}MnO{sub 3} with different size prepared via a facile microwave-assisted method. - Highlights: • Nanoparticles of La{sub 0.8}Sr{sub 0.2}MnO{sub 3} were synthesized by the microwave irradiation process. • The structural studies show that all samples crystallize in a rhombohedral structure with space group of R−3C. • The DC magnetic studies confirm tuning of the magnetic properties due to the particle size effects.
AC Application of HTS Conductors in Highly Dynamic Electric Motors
NASA Astrophysics Data System (ADS)
Oswald, B.; Best, K.-J.; Setzer, M.; Duffner, E.; Soell, M.; Gawalek, W.; Kovalev, L. K.
2006-06-01
Based on recent investigations we design highly dynamic electric motors up to 400 kW and linear motors up to 120 kN linear force using HTS bulk material and HTS tapes. The introduction of HTS tapes into AC applications in electric motors needs fundamental studies on double pancake coils under transversal magnetic fields. First theoretical and experimental results on AC field distributions in double-pancake-coils and corresponding AC losses will be presented. Based on these results the simulation of the motor performance confirms extremely high power density and efficiency of both types of electric motors. Improved characteristics of rare earth permanent magnets used in our motors at low temperatures give an additional technological benefit.
Detection of magnetic nanoparticles with a large scale AC superconducting susceptometer
NASA Astrophysics Data System (ADS)
Hincapie Ladino, E. A.; Zufelato, N.; Bakuzis, A. F.; Oliveira Carneiro, A. A.; Covas, D. T.; Baffa, O.
2017-08-01
Magnetic nanoparticles (MNPs) are being used in several applications in medicine such as hyperthermia, magnetic particle imaging, in vitro and in vivo bioassay, and still there are many other possibilities for use of these particles to come as research progress in this field. One crucial step of its use is the detection of these particles when present in a certain tissue. For in vitro bioassay, the sample can be harvested and placed inside the detector in optimal conditions to favor sensitivity. However, for in vivo human measurements the system must be noninvasive and conform to the anatomic restrictions requiring sensitive detectors and dedicated setups. In this study, we detect nanoparticles with an AC biosusceptometer having an excitation homogeneous magnetic field with 145 μT, provided by a set of rectangular large Rubens coils driven at 10 Hz. The magnetization induced in the sample was detected by a second-order axial gradiometer (20 mm in diameter and 40 mm of baseline) coupled to an RF Superconducting Quantum Interference Device (SQUID) model 330X (BTi). The MNPs used were manganese ferrite-based surface-coated with citric acid ({{M}}{{n}}{{F}}{{{e}}}2{{{O}}}4-{{C}}{{i}}{{t}}{{r}}{{a}}{{t}}{{e}}), dissolved in water at various concentrations. The colloid is stable at physiological conditions. X-ray diffraction confirmed the spinel structure and using Scherrer’s relation revealed a particle size of 17.3 nm. The magnetization curve showed a typical superparamagnetic behavior with a specific saturation magnetization of 51.2 emu g-1. The stock solution of nanoparticles had a concentration of 23.17 mg ml-1, corresponding to 1.7 × 1015 NPs ml-1. Measurements were made in a volume of 30 ml with 20 × 103-100 × 103 dilutions of the stock solution of nanoparticles and performed at distances of 1.1, 1.5 and 2.5 cm from the top of the sample vial to the closest coil of the gradiometer. The limits of detection were 8.1 × 109 NP ml-1, 9.5 × 109 NP ml-1 and 11
NASA Astrophysics Data System (ADS)
Lu, Wei; Huang, Ping; Wang, Yuxin; Yan, Biao
2013-07-01
In this paper, Nb element was partially replaced by V element in Finemet-type Fe73Cu1Nb3.5-xVxSi13.5B9 (x = 1, 1.5, 2) alloys and the effect of annealing temperatures on the microstructure and AC magnetic properties of the samples are studied. The annealing temperatures affect the grain sizes of the bcc α-Fe phase greatly. When the annealing temperature is between 540-560°C, the samples have better AC magnetic properties than the samples annealed at other temperatures. The optimized annealing temperature of the studied samples is around 560°C. The coercivity and iron loss of the V2 sample is a little bit higher than that of V1 and V1.5 alloys while the amplitude permeability of V2 alloy is larger than that of V1 and V1.5, which indicate that the content of V element has strong influence on the magnetic properties of nanocrystalline soft magnetic alloys.
Microwave ac Zeeman force for ultracold atoms
NASA Astrophysics Data System (ADS)
Fancher, C. T.; Pyle, A. J.; Rotunno, A. P.; Aubin, S.
2018-04-01
We measure the ac Zeeman force on an ultracold gas of 87Rb due to a microwave magnetic field targeted to the 6.8 GHz hyperfine splitting of these atoms. An atom chip produces a microwave near field with a strong amplitude gradient, and we observe a force over three times the strength of gravity. Our measurements are consistent with a simple two-level theory for the ac Zeeman effect and demonstrate its resonant, bipolar, and spin-dependent nature. We observe that the dressed-atom eigenstates gradually mix over time and have mapped out this behavior as a function of magnetic field and detuning. We demonstrate the practical spin selectivity of the force by pushing or pulling a specific spin state while leaving other spin states unmoved.
Imaging ac losses in superconducting films via scanning Hall probe microscopy
NASA Astrophysics Data System (ADS)
Dinner, Rafael B.; Moler, Kathryn A.; Feldmann, D. Matthew; Beasley, M. R.
2007-04-01
Various local probes have been applied to understanding current flow through superconducting films, which are often surprisingly inhomogeneous. Here, we show that magnetic imaging allows quantitative reconstruction of both current density J and electric field E resolved in time and space in a film carrying subcritical ac current. Current reconstruction entails inversion of the Biot-Savart law, while electric fields are reconstructed using Faraday’s law. We describe the corresponding numerical procedures, largely adapting existing work to the case of a strip carrying ac current, but including other methods of obtaining the complete electric field from the inductive portion determined by Faraday’s law. We also delineate the physical requirements behind the mathematical transformations. We then apply the procedures to images of a strip of YBa2Cu3O7-δ carrying an ac current at 400Hz . Our scanning Hall probe microscope produces a time series of magnetic images of the strip with 1μm spatial resolution and 25μs time resolution. Combining the reconstructed J and E , we obtain a complete characterization including local critical current density, E-J curves, and power losses. This analysis has a range of applications from fundamental studies of vortex dynamics to practical coated conductor development.
Spectroscopy of Magnetic Excitations in Magnetic Superconductors Using Vortex Motion
NASA Astrophysics Data System (ADS)
Bulaevskii, L. N.; Hruška, M.; Maley, M. P.
2005-11-01
In magnetic superconductors a moving vortex lattice is accompanied by an ac magnetic field which leads to the generation of spin waves. At resonance conditions the dynamics of vortices in magnetic superconductors changes drastically, resulting in strong peaks in the dc I-V characteristics at voltages at which the washboard frequency of the vortex lattice matches the spin wave frequency ωs(g), where g are the reciprocal vortex lattice vectors. We show that if the washboard frequency lies above the magnetic gap, measurement of the I-V characteristics provides a new method to obtain information on the spectrum of magnetic excitations in borocarbides and cuprate layered magnetic superconductors.
Artificial neural networks for AC losses prediction in superconducting round filaments
NASA Astrophysics Data System (ADS)
Leclerc, J.; Makong Hell, L.; Lorin, C.; Masson, P. J.
2016-06-01
An extensive and fast method to estimate superconducting AC losses within a superconducting round filament carrying an AC current and subjected to an elliptical magnetic field (both rotating and oscillating) is presented. Elliptical fields are present in rotating machine stators and being able to accurately predict AC losses in fully superconducting machines is paramount to generating realistic machine designs. The proposed method relies on an analytical scaling law (ASL) combined with two artificial neural network (ANN) estimators taking 9 input parameters representing the superconductor, external field and transport current characteristics. The ANNs are trained with data generated by finite element (FE) computations with a commercial software (FlexPDE) based on the widely accepted H-formulation. After completion, the model is validated through comparison with additional randomly chosen data points and compared for simple field configurations to other predictive models. The loss estimation discrepancy is about 3% on average compared to the FEA analysis. The main advantages of the model compared to FE simulations is the fast computation time (few milliseconds) which allows it to be used in iterated design processes of fully superconducting machines. In addition, the proposed model provides a higher level of fidelity than the scaling laws existing in literature usually only considering pure AC field.
NASA Astrophysics Data System (ADS)
Honke, Michael L.; Bidinosti, Christopher P.
2018-06-01
We describe a very simple experiment that utilizes standard laboratory equipment to measure the electromagnetic response of a metallic sphere exposed to a uniform ac magnetic field. Measurements were made for a variety of non-magnetic and magnetic metals, and in all cases the results fit very well with theory over the four orders of frequency (25 Hz to 102 kHz) explored here. Precise values of magnetic permeability and electrical conductivity can be extracted from fits to the data given the sphere radius only. The same apparatus is also used to explore the effects of geometry on eddy current generation as well as to demonstrate non-destructive testing through measurements on coins of different composition.
Characterizing fiber-reinforced composite structures using AC-impedance spectroscopy (AC-IS)
NASA Astrophysics Data System (ADS)
Woo, Leta Y.
Property enhancement in composites depends largely on the reinforcement. For fiber-reinforced composites, the distribution of fibers is crucial in determining the electrical and mechanical performance. Image analysis methods for characterization can be time-consuming and/or destructive. This work explores the capability of AC-impedance spectroscopy (AC-IS), an electrical measurement technique, to serve as a rapid, non-destructive tool for characterizing composite microstructure. The composite requirements include a filler that is electrically conducting or semi-conducting with higher conductivity than the matrix, and a high-impedance interface or coating between the filler and the matrix. To establish an AC-IS characterization method, cement-matrix composites with steel reinforcement were employed as both a technologically important and a model system to investigate how fibers affect the electrical response. Beginning with spherical particulates and then fibers, composites were examined using composite theory and an "intrinsic conductivity" approach. The intrinsic conductivity approach applies to composites with low volume fractions of fibers (i.e., in the dilute regime) and relates how the composite conductivity varies relative to the matrix as a function of volume fraction. A universal equivalent circuit model was created to understand the AC-IS response of composites based on the geometry and volume fraction of the filler. Deviation from predicted behavior was assessed using a developed f-function, which quantifies how fibers contribute to the overall electrical response of the composite. Using the f-function, an AC-IS method for investigating fiber dispersion was established to characterize alignment, settling/segregation, and aggregation. Alignment was investigated using measurements made in three directions. A point-probe technique characterized settling and/or large-scale inhomogeneous mixing in samples. Aggregation was quantified using a "dispersion factor
Lu, Bin [Kenosha, WI; Luebke, Charles John [Sussex, WI; Habetler, Thomas G [Snellville, GA; Zhang, Pinjia [Atlanta, GA; Becker, Scott K [Oak Creek, WI
2011-12-27
A system and method for measuring and controlling stator winding temperature in an AC motor while idling is disclosed. The system includes a circuit having an input connectable to an AC source and an output connectable to an input terminal of a multi-phase AC motor. The circuit further includes a plurality of switching devices to control current flow and terminal voltages in the multi-phase AC motor and a controller connected to the circuit. The controller is configured to activate the plurality of switching devices to create a DC signal in an output of the motor control device corresponding to an input to the multi-phase AC motor, determine or estimate a stator winding resistance of the multi-phase AC motor based on the DC signal, and estimate a stator temperature from the stator winding resistance. Temperature can then be controlled and regulated by DC injection into the stator windings.
Methods for Addressing Missing Data with Applications from ACS Exams
ERIC Educational Resources Information Center
Brandriet, Alexandra; Holme, Thomas
2015-01-01
As part of the ACS Examinations Institute (ACS-EI) national norming process, student performance data sets are collected from professors at colleges and universities from around the United States. Because the data sets are collected on a volunteer basis, the ACS-EI often receives data sets with only students' total scores and without the students'…
A critical comparison of electrical methods for measuring spin-orbit torques
NASA Astrophysics Data System (ADS)
Zhang, Xuanzi; Hung, Yu-Ming; Rehm, Laura; Kent, Andrew D.
Direct (DC) and alternating current (AC) transport measurements of spin-orbit torques (SOTs) in heavy metal-ferromagnet heterostructure with perpendicular magnetic anisotropy have been proposed and demonstrated. A DC method measures the change of perpendicular magnetization component while an AC method probes the first and second harmonic magnetization oscillation in responses to an AC current (~1 kHz). Here we conduct both types of measurements on β-Ta/CoFeB/MgO in the form of patterned Hall bars (20 μm linewidth) and compare the results. Experiments results are qualitatively in agreement with a macro spin model including Slonzewski-like and a field-like SOTs. However, the effective field from the ac method is larger than that obtained from the DC method. We discuss the possible origins of the discrepancy and its implications for quantitatively determining SOTs. Research supported by the SRC-INDEX program, NSF-DMR-1309202 and NYU-DURF award.
Efficiency estimation method of three-wired AC to DC line transfer
NASA Astrophysics Data System (ADS)
Solovev, S. V.; Bardanov, A. I.
2018-05-01
The development of power semiconductor converters technology expands the scope of their application to medium voltage distribution networks (6-35 kV). Particularly rectifiers and inverters of appropriate power capacity complement the topology of such voltage level networks with the DC links and lines. The article presents a coefficient that allows taking into account the increase of transmission line capacity depending on the parameters of it. The application of the coefficient is presented by the example of transfer three-wired AC line to DC in various methods. Dependences of the change in the capacity from the load power factor of the line and the reactive component of the resistance of the transmission line are obtained. Conclusions are drawn about the most efficient ways of converting a three-wired AC line to direct current.
Dielectric and magnetic studies of Cr+3 doped nickel ferrite by combustion method
NASA Astrophysics Data System (ADS)
Parveez, Asiya; Shekhawat, M. S.; Sindhu, S.; Srikanth, C.; Nayeem, Firdous; Mohd. Shariff, S.; Sinha, R. R.; Chaudhuri, Arka; Khader, S. Abdul
2018-05-01
Cr+3 doped nickel ferrite nanoparticles having the basic composition NiCrxFe2-xO4 (x=0, 0.1, 0.15, 0.2, 1) were prepared using auto combustion method. Structural, dielectric, a.c conductivity and magnetic properties of these samples, which are sintered at 800°C were studied. The structures of the synthesized samples were probed by X-ray diffraction (XRD) studies. The peaks observed in the XRD spectrum indicated single phase spinel cubic structure for the synthesized samples. Surface morphology of the samples has been investigated using Field Emission Scanning Electron Microscope (FESEM). The dielectric constant (ɛ') and dielectric loss factor (ɛ″) of nanocrystalline nickel ferrites were investigated as a function of frequency and Cr+3 concentration at room temperature over the frequency range 100 Hz to 1 MHz using Hioki make LCR Hi-Tester 3250. The dependence of ɛ' and ɛ″ with the frequency of the alternating applied electric field is in accordance with the Maxwell-Wagner type interfacial polarization, which is in agreement with the Koop's theory. The electrical conductivity (σac) deduced from the measured dielectric data has been thoroughly analyzed and found that the conduction mechanism in NiCrxFe2-xO4 nanoferrites are in conformity with the electron hopping model. The magnetic properties of Cr+3 doped nano-nickel ferrite were analyzed using a Vibrating Sample Magnetometer (VSM). It is observed that the values of saturation magnetization decreases along with the increase in chromium content.
Muehsam, David J; Pilla, Arthur A
2009-09-01
We have previously employed the Lorentz-Langevin model to describe the effects of weak exogenous magnetic fields via the classical Lorentz force on a charged ion bound in a harmonic oscillator potential, in the presence of thermal noise forces. Previous analyses predicted that microT-range fields give rise to a rotation of the oscillator orientation at the Larmor frequency and bioeffects were based upon the assumption that the classical trajectory of the bound charge itself could modulate a biochemical process. Here, it is shown that the thermal component of the motion follows the Larmor trajectory. The results show that the Larmor frequency is independent of the thermal noise strength, and the motion retains the form of a coherent oscillator throughout the binding lifetime, rather than devolving into a random walk. Thermal equilibration results in a continual increase in the vibrational amplitude of the rotating oscillator towards the steady-state amplitude, but does not affect the Larmor orbit. Thus, thermal noise contributes to, rather than inhibits, the effect of the magnetic field upon reactivity. Expressions are derived for the ensemble average of position and the velocity of the thermal component of the oscillator motion. The projection of position and velocity onto a Cartesian axis measures the nonuniformity of the Larmor trajectory and is illustrated for AC and combined AC/DC magnetic fields, suggesting a means of interpreting resonance phenomena. It is noted that the specific location and height of resonances are dependent upon binding lifetime and initial AC phase.
Das, R; Rinaldi-Montes, N; Alonso, J; Amghouz, Z; Garaio, E; García, J A; Gorria, P; Blanco, J A; Phan, M H; Srikanth, H
2016-09-28
Over the past two decades, magnetic hyperthermia and photothermal therapy are becoming very promising supplementary techniques to well-established cancer treatments such as radiotherapy and chemotherapy. These techniques have dramatically improved their ability to perform controlled treatments, relying on the procedure of delivering nanoscale objects into targeted tumor tissues, which can release therapeutic killing doses of heat either upon AC magnetic field exposure or laser irradiation. Although an intense research effort has been made in recent years to study, separately, magnetic hyperthermia using iron oxide nanoparticles and photothermal therapy based on gold or silver plasmonic nanostructures, the full potential of combining both techniques has not yet been systematically explored. Here we present a proof-of-principle experiment showing that designing multifunctional silver/magnetite (Ag/Fe3O4) nanoflowers acting as dual hyperthermia agents is an efficient route for enhancing their heating ability or specific absorption rate (SAR). Interestingly, the SAR of the nanoflowers is increased by at least 1 order of magnitude under the application of both an external magnetic field of 200 Oe and simultaneous laser irradiation. Furthermore, our results show that the synergistic exploitation of the magnetic and photothermal properties of the nanoflowers reduces the magnetic field and laser intensities that would be required in the case that both external stimuli were applied separately. This constitutes a key step toward optimizing the hyperthermia therapy through a combined multifunctional magnetic and photothermal treatment and improving our understanding of the therapeutic process to specific applications that will entail coordinated efforts in physics, engineering, biology, and medicine.
Ehmler, Hartmut; Köppen, Matthias
2007-10-01
The impedance spectrum test was employed for detection of short circuits within Wendelstein 7-X (W7-X) superconducting magnetic field coils. This test is based on measuring the complex impedance over several decades of frequency. The results are compared to predictions of appropriate electrical equivalent circuits of coils in different production states or during cold test. When the equivalent circuit is not too complicated the impedance can be represented by an analytic function. A more detailed analysis is performed with a network simulation code. The overall agreement of measured and calculated or simulated spectra is good. Two types of short circuits which appeared are presented and analyzed. The detection limit of the method is discussed. It is concluded that combined high-voltage ac and low-voltage impedance spectrum tests are ideal means to rule out short circuits in the W7-X coils.
Vrijsen, N H; Jansen, J W; Compter, J C; Lomonova, E A
2013-07-01
A measurement method is presented which identifies the magnetic hysteresis effects present in the force of linear reluctance actuators. The measurement method is applied to determine the magnetic hysteresis in the force of an E-core reluctance actuator, with and without pre-biasing permanent magnet. The force measurements are conducted with a piezoelectric load cell (Kistler type 9272). This high-bandwidth force measurement instrument is identified in the frequency domain using a voice-coil actuator that has negligible magnetic hysteresis and eddy currents. Specifically, the phase delay between the current and force of the voice-coil actuator is used for the calibration of the measurement instrument. This phase delay is also obtained by evaluation of the measured force and flux variation in the E-core actuator, both with and without permanent magnet on the middle tooth. The measured magnetic flux variation is used to distinguish the phase delay due to magnetic hysteresis from the measured phase delay between the current and the force of the E-core actuator. Finally, an open loop steady-state ac model is presented that predicts the magnetic hysteresis effects in the force of the E-core actuator.
NASA Astrophysics Data System (ADS)
Mancusi, D.; Polichetti, M.; Cimberle, M. R.; Pace, S.
2015-09-01
The temperature-dependent fundamental ac susceptibility of a granular superconductor in the absence of dc fields has been analyzed by developing a phenomenological model for effective magnetic fields, taking into account the influence of the magnetic interaction between the intergranular and the intragranular magnetizations due to demagnetizing effects. For this purpose a policrystal Fe-based superconductor FeSe0.5Te0.5 sample has been studied. By the frequency dependence of the peaks of the temperature-dependent imaginary part of the fundamental complex susceptibility, the dependence on temperature of the characteristic times both for intergranular and intragranular relaxations of magnetic flux are derived, and the corresponding relaxation processes due to combinations of the flux creep, the flux flow and the thermally activated flux flow regimes are identified on the basis of the effective magnetic fields both at the sample surface and at the grains’ surfaces. Such characteristic times, through the Havriliak-Negami function, determine the temperature and the frequency dependences of the complex susceptibility. The comparison of the numerically obtained curves with the experimental ones confirms the relevance, for identifying the intergranular and intragranular contributions to the ac magnetic response and the corresponding flux dynamical regimes, of the interaction between the intergranular and intragranular magnetizations due to demagnetizing effects.
NASA Astrophysics Data System (ADS)
Hu, Xiaojing; Li, Qiang; Zhang, Hao; Guo, Ziming; Zhao, Kun; Li, Xinpeng
2018-06-01
Based on the Monte Carlo method, an improved risk assessment method for hybrid AC/DC power system with VSC station considering the operation status of generators, converter stations, AC lines and DC lines is proposed. According to the sequential AC/DC power flow algorithm, node voltage and line active power are solved, and then the operation risk indices of node voltage over-limit and line active power over-limit are calculated. Finally, an improved two-area IEEE RTS-96 system is taken as a case to analyze and assessment its operation risk. The results show that the proposed model and method can intuitively and directly reflect the weak nodes and weak lines of the system, which can provide some reference for the dispatching department.
NASA Technical Reports Server (NTRS)
Linley, L. J.; Luper, A. B.; Dunn, J. H.
1982-01-01
The Bureau of Mines, U.S. Department of the Interior, is reviewing explosion protection methods for use in gassy coal mines. This performance criteria guideline is an evaluation of three explosion protection methods of machines electrically powered with voltages up to 15,000 volts ac. A sufficient amount of basic research has been accomplished to verify that the explosion proof and pressurized enclosure methods can provide adequate explosion protection with the present state of the art up to 15,000 volts ac. This routine application of the potted enclosure as a stand alone protection method requires further investigation or development in order to clarify performance criteria and verification certification requirements. An extensive literature search, a series of high voltage tests, and a design evaluation of the three explosion protection methods indicate that the explosion proof, pressurized, and potted enclosures can all be used to enclose up to 15,000 volts ac.
Simultaneous distribution of AC and DC power
Polese, Luigi Gentile
2015-09-15
A system and method for the transport and distribution of both AC (alternating current) power and DC (direct current) power over wiring infrastructure normally used for distributing AC power only, for example, residential and/or commercial buildings' electrical wires is disclosed and taught. The system and method permits the combining of AC and DC power sources and the simultaneous distribution of the resulting power over the same wiring. At the utilization site a complementary device permits the separation of the DC power from the AC power and their reconstruction, for use in conventional AC-only and DC-only devices.
Method And Apparatus For Production Of Bi-213 From The Activity Ac-225 Source
Egorov, Oleg B.; O'Hara, Matthew J.
2005-12-06
A method and apparatus for isolating and purifying a .sup.213 Bi radioactive isotope from an .sup.225 Ac source using a primary column and a primary sorbent which preferentially retains .sup.225 Ac over .sup.213 Bi when exposed to a compatible solvent in combination with a secondary column having a secondary sorbent which retains .sup.213 Bi when exposed to a mixture of the compatible solvent and .sup.213 Bi. A "compatible solvent" is a solvent which will preferentially remove .sup.213 Bi radioactive isotopes from a primary sorbent without removing .sup.225 Ac radioactive isotopes, and then allow .sup.213 Bi radioactive isotopes removed from the primary sorbent to be retained on a secondary sorbent, without having to dilute or otherwise chemically or physically modify the compatible solvent in between exposure to the primary and secondary sorbents.
Modeling of screening currents in coated conductor magnets containing up to 40000 turns
NASA Astrophysics Data System (ADS)
Pardo, E.
2016-08-01
Screening currents caused by varying magnetic fields degrade the homogeneity and stability of the magnetic fields created by REBCO coated conductor coils. They are responsible for the AC loss; which is also important for other power applications containing windings, such as transformers, motors and generators. Since real magnets contain coils exceeding 10000 turns, accurate modeling tools for this number of turns or above are necessary for magnet design. This article presents a fast numerical method to model coils with no loss of accuracy. We model a 10400-turn coil for its real number of turns and coils of up to 40000 turns with continuous approximation, which introduces negligible errors. The screening currents, the screening current induced field (SCIF) and the AC loss is analyzed in detail. The SCIF is at a maximum at the remnant state with a considerably large value. The instantaneous AC loss for an anisotropic magnetic-field dependent J c is qualitatively different than for a constant J c , although the loss per cycle is similar. Saturation of the magnetization currents at the end pancakes causes the maximum AC loss at the first ramp to increase with J c . The presented modeling tool can accurately calculate the SCIF and AC loss in practical computing times for coils with any number of turns used in real windings, enabling parameter optimization.
NASA Astrophysics Data System (ADS)
Prando, G.; Carretta, P.; de Renzi, R.; Sanna, S.; Palenzona, A.; Putti, M.; Tropeano, M.
2011-05-01
Ac susceptibility and static magnetization measurements were performed in the optimally doped SmFeAsO0.8F0.2 superconductor. The field-temperature phase diagram of the superconducting state was drawn, and, in particular, the features of the flux lines were derived. The dependence of the intragrain depinning energy on the magnetic field intensity was derived in the thermally activated flux-creep framework, enlightening a typical 1/H dependence in the high-field regime. The intragrain critical current density was extrapolated in the zero-temperature and zero-magnetic-field limit, showing a remarkably high value Jc0(0)~2×107 A/cm2, which demonstrates that this material is rather interesting for potential future technological applications.
AC Loss Minimization in High Temperature Superconductors - U.K.
2003-11-07
high currents in high magnetic fields. The DC properties are very attractive, but to reduce the AC losses it is necessary to use a narrow conductor... NiFe in the whole magnetic field region (goHext=0.01 T - 6 T) roughly by a factor of 2, reflecting the sample Jc(B) dependencies. Also the magnetic ...ratio of the tape, there is no visible effect in a parallel magnetic field. Hysteresis losses in metallic substrates - CeO2:Pd/ NiFe and CeO2:Pd/NiCrW
Magnetostrictive materials and method for improving AC characteristics in same
Pulvirenti, Patricia P.; Jiles, David C.
2001-08-14
The present invention provides Terfenol-D alloys ("doped" Terfenol) having optimized performances under the condition of time-dependent magnetic fields. In one embodiment, performance is optimized by lowering the conductivity of Terfenol, thereby improving the frequency response. This can be achieved through addition of Group III or IV elements, such as Si and Al. Addition of these types of elements provides scattering sites for conduction electrons, thereby increasing resistivity by 125% which leads to an average increase in penetration depth of 80% at 1 kHz and an increase in energy conversion efficiency of 55%. The permeability of doped Terfenol remains constant over a wider frequency range as compared with undoped Terfenol. These results demonstrate that adding impurities, such as Si and Al, are effective in improving the ac characteristics of Terfenol. A magnetoelastic Gruneisen parameter, .gamma..sub.me, has also been derived from the thermodynamic equations of state, and provides another means by which to characterize the coupling efficiency in magnetostrictive materials on a more fundamental basis.
Introducing AC inductive reactance with a power tool
NASA Astrophysics Data System (ADS)
Bryant, Wesley; Baker, Blane
2016-09-01
The concept of reactance in AC electrical circuits is often non-intuitive and difficult for students to grasp. In order to address this lack of conceptual understanding, classroom exercises compare the predicted resistance of a power tool, based on electrical specifications, to measured resistance. Once students discover that measured resistance is smaller than expected, they are asked to explain these observations using previously studied principles of magnetic induction. Exercises also introduce the notion of inductive reactance and impedance in AC circuits and, ultimately, determine self-inductance of the motor windings within the power tool.
NASA Astrophysics Data System (ADS)
Cao, Jia; Yan, Zheng; He, Guangyu
2016-06-01
This paper introduces an efficient algorithm, multi-objective human learning optimization method (MOHLO), to solve AC/DC multi-objective optimal power flow problem (MOPF). Firstly, the model of AC/DC MOPF including wind farms is constructed, where includes three objective functions, operating cost, power loss, and pollutant emission. Combining the non-dominated sorting technique and the crowding distance index, the MOHLO method can be derived, which involves individual learning operator, social learning operator, random exploration learning operator and adaptive strategies. Both the proposed MOHLO method and non-dominated sorting genetic algorithm II (NSGAII) are tested on an improved IEEE 30-bus AC/DC hybrid system. Simulation results show that MOHLO method has excellent search efficiency and the powerful ability of searching optimal. Above all, MOHLO method can obtain more complete pareto front than that by NSGAII method. However, how to choose the optimal solution from pareto front depends mainly on the decision makers who stand from the economic point of view or from the energy saving and emission reduction point of view.
NASA Astrophysics Data System (ADS)
Dhani, H. S.; Aminudin, A.; Waslaluddin
2018-05-01
Electric current is the basic variable of measurement in instrumentation system. One of the current measurements had been developed was based on magnetic sensor. Giant Magnetoresistance (GMR) produces an output voltage when it detects the magnetic field from electric current flow. The purpose of this study was to characterize the response of GMR when variation number of coil was given. The characterization was the GMR voltage response to the AC current values from 0.01 A to 5.00 A. The linearity of the relation was reaching saturation point when the magnetic field measured higher than 10.5 Oe at room temperature. As the number of coil increased, the earlier saturation occurred. To see the sensitivity of the sensor response, the data graph was cut off at 1.56 A AC. From this research, we got single coil was ideal to measure electric current higher than 1.56 A AC, as the relation of GMR voltage to the current tended to maintain its linearity. For measurement of 1.56 A AC and less, coil number addition would increase the sensitivity of sensor response. This research hopefully will be benefit for further development using an electric current measurement based on GMR magnetic sensor for power meter design.
NASA Astrophysics Data System (ADS)
Yang, C. C.; Yang, S. Y.; Chen, H. H.; Weng, W. L.; Horng, H. E.; Chieh, J. J.; Hong, C. Y.; Yang, H. C.
2012-07-01
By specifically bio-functionalizing magnetic nanoparticles, magnetic nanoparticles are able to label target bio-molecules. This property can be applied to quantitatively detect molecules invitro by measuring the related magnetic signals of nanoparticles bound with target molecules. One of the magnetic signals is the reduction in the mixed-frequency ac magnetic susceptibility of suspended magnetic nanoparticles due to the molecule-particle association. Many experimental results show empirically that the molecular-concentration dependent reduction in ac magnetic susceptibility follows the logistic function. In this study, it has been demonstrated that the logistic behavior is originated from the growth of particle sizes due to the molecule-particle association. The analytic relationship between the growth of particle sizes and the reduction in ac magnetic susceptibility is developed.
NASA Astrophysics Data System (ADS)
Hikosaka, Tomoyuki; Miyamoto, Masahiro; Yamada, Mamoru; Morita, Tadashi
1993-05-01
It is very important to obtain saturated magnetic properties from reverse saturation (full B-H curve) of ferromagnetic cores to design magnetic switches which are used in high power pulse generators. The magnetic switch is excited in the high frequency range (˜MHz). But, it is extremely difficult to measure full B-H curve of large toroidal cores of which diameter is some hundreds of mm, using the conventional ac excitation method at high frequency. The main reason is poor output ability of power source for core excitation. Therefore we have developed pulse excitation method to get high frequency magnetic properties. The measurement circuit has two sections. One is excitation part composed by charge transfer circuit. The others is reset part for adjustment initial point on direct B-H curve. The sample core is excited by sinusoidal voltage pulse expressed as 1-cos(2π ft). Excitation frequency f is decided by the constants of the elements of the charge transfer circuit. The change of magnetic flux density ΔB and magnetic field H are calculated, respectively, by measuring the induced voltage of search coil and magnetizing current. ΔB-H characteristics from reverse saturation of four different kinds of large cores were measured in frequency range from 50 kHz to 1 MHz. Core loss increases in proportion to Nth powers of the frequency, where the index N depends on each of cores. N is about 0.5 in case of winding ribbon cores, such as Fe-based amorphous, Co-based amorphous, and Finemet, but N is about 0.2 in case of the Ni-Zn ferrite.
Hamiltonian methods of modeling and control of AC microgrids with spinning machines and inverters
DOE Office of Scientific and Technical Information (OSTI.GOV)
Matthews, Ronald C.; Weaver, Wayne W.; Robinett, Rush D.
This study presents a novel approach to the modeling and control of AC microgrids that contain spinning machines, power electronic inverters and energy storage devices. The inverters in the system can adjust their frequencies and power angles very quickly, so the modeling focuses on establishing a common reference frequency and angle in the microgrid based on the spinning machines. From this dynamic model, nonlinear Hamiltonian surface shaping and power flow control method is applied and shown to stabilize. From this approach the energy flow in the system is used to show the energy storage device requirements and limitations for themore » system. This paper first describes the model for a single bus AC microgrid with a Hamiltonian control, then extends this model and control to a more general class of multiple bus AC microgrids. Finally, simulation results demonstrate the efficacy of the approach in stabilizing and optimization of the microgrid.« less
Hamiltonian methods of modeling and control of AC microgrids with spinning machines and inverters
Matthews, Ronald C.; Weaver, Wayne W.; Robinett, Rush D.; ...
2017-12-22
This study presents a novel approach to the modeling and control of AC microgrids that contain spinning machines, power electronic inverters and energy storage devices. The inverters in the system can adjust their frequencies and power angles very quickly, so the modeling focuses on establishing a common reference frequency and angle in the microgrid based on the spinning machines. From this dynamic model, nonlinear Hamiltonian surface shaping and power flow control method is applied and shown to stabilize. From this approach the energy flow in the system is used to show the energy storage device requirements and limitations for themore » system. This paper first describes the model for a single bus AC microgrid with a Hamiltonian control, then extends this model and control to a more general class of multiple bus AC microgrids. Finally, simulation results demonstrate the efficacy of the approach in stabilizing and optimization of the microgrid.« less
NASA Astrophysics Data System (ADS)
Kumar, Pawan; Cao, Yongze; Suzuki, Yudai; Yoshimura, Satoru; Saito, Hitoshi
2018-06-01
In this report, the magnetic energy flow of AC magnetic field is imaged from a perpendicular magnetic recording head by alternating magnetic force microscopy (A-MFM) with high magnetic moment Co0.43(GdOx)0.57 superparamagnetic (SP) tip. The present magnetic energy flow imaging phenomenon is able to detect the flow direction of AC magnetic field energy from the recording head. A simple model for the flow direction of the AC magnetic energy is given and revealed that when the AC magnetic field energy from the surface of main pole increases, the energy from the side cross section decreases due to the periodical change of magnetization direction at the main pole area. The A-MFM magnetic energy imaging performance by 100 nm Co0.43(GdOx)0.57 SP tip is compared with the magnetic field imaging with the 25 nm Co0.80Zr0.05Nb0.15 soft magnetic (SM) tip. The spatial resolution measured by Fourier analysis for Co0.43(GdOx)0.57 SP tip is enhanced dramatically to ˜10 nm with low thermal noise, as compared to ˜13 nm by Co0.80Zr0.05Nb0.15 SM tip as well as the previously reported MFM tip. Moreover, the sensitivity and resolution are investigated for a range of head current to confirm the suitability of the magnetic energy flow imaging by Co0.43(GdOx)0.57 SP tip to low as well as high magnetic field source. Further, the A-MFM measurements are performed with the 100 nm Au coated conducting tip to investigate the possibility of electrostatic contribution in magnetic energy imaging by Co0.43(GdOx)0.57 SP tip and revealed that the present A-MFM measurement is free from any electrostatic artifacts. The present magnetic energy flow imaging phenomena with the high magnetic moment Co0.43(GdOx)0.57 SP tip provides an avenue for the analysis of the magnetic field energy component from the head field profile.
Modeling AC ripple currents in HTS coated conductors by integral equations
NASA Astrophysics Data System (ADS)
Grilli, Francesco; Xu, Zhihan
2016-12-01
In several HTS applications, the superconducting tapes experience the simultaneous presence of DC and AC excitations. For example in high-current DC cables, where the transport current is not perfectly constant, but it exhibits some ripples at different frequencies introduced by the rectification process (AC-DC conversion). These ripples give rise to dissipation, whose magnitude and possible influence on the device's cooling requirements need to be evaluated. Here we report a study of the AC losses in a HTS coated conductor subjected to DC currents and AC ripples simultaneously. The modeling approach is based on an integral equation method for thin superconductors: the superconducting tape is modeled as a 1-D object with a non-linear resistivity, which includes the dependence of the critical current density Jc on the magnetic field. The model, implemented in a commercial finite-element program, runs very fast (the simulation of one AC cycle typically takes a few seconds on standard desktop workstation): this allows simulating a large number of cycles and estimating when the AC ripple losses stabilize to a constant value. The model is used to study the influence of the flux creep power index n on the stabilization speed and on the AC loss values, as well as the effect of using a field-dependent Jc instead of a constant one. The simulations confirm that the dissipation level should not be a practical concern in HTS DC cables. At the same time, however, they reveal a strong dependence of the results upon the power index n and the form of Jc , which spurs the question whether the power-law is the most suitable description of the superconductor's electrical behavior for this kind of analysis.
Monitoring of changes in cluster structures in water under AC magnetic field
NASA Astrophysics Data System (ADS)
Usanov, A. D.; Ulyanov, S. S.; Ilyukhina, N. S.; Usanov, D. A.
2016-01-01
A fundamental possibility of visualizing cluster structures formed in distilled water by an optical method based on the analysis of dynamic speckle structures is demonstrated. It is shown for the first time that, in contrast to the existing concepts, water clusters can be rather large (up to 200 -m in size), and their lifetime is several tens of seconds. These clusters are found to have an internal spatially inhomogeneous structure, constantly changing in time. The properties of magnetized and non-magnetized water are found to differ significantly. In particular, the number of clusters formed in magnetized water is several times larger than that formed in the same volume of non-magnetized water.
Taboada-Serrano, Patricia; Tsouris, Constantino; Contescu, Cristian I; McFarlane, Joanna
2013-10-08
The present invention provides magnetically responsive activated carbon, and a method of forming magnetically responsive activated carbon. The method of forming magnetically responsive activated carbon typically includes providing activated carbon in a solution containing ions of ferrite forming elements, wherein at least one of the ferrite forming elements has an oxidation state of +3 and at least a second of the ferrite forming elements has an oxidation state of +2, and increasing pH of the solution to precipitate particles of ferrite that bond to the activated carbon, wherein the activated carbon having the ferrite particles bonded thereto have a positive magnetic susceptibility. The present invention also provides a method of filtering waste water using magnetic activated carbon.
NASA Astrophysics Data System (ADS)
Mori, Hiroshi; Asahara, Yousuke
1996-03-01
We analyze the linearity and modulation depth of ac magnetic-field sensors or current sensors, using a ferrimagnetic or ferromagnetic film as the Faraday rotator and employing the detection of only the zeroth-order optical diffraction component from the rotator. It is theoretically shown that for this class of sensor the condition of a constant modulation depth and that of a constant ratio error give an identical series of curves for the relationship between Faraday rotation angle greater than or equals V and polarizer/analyzer relative angle Phi . We give some numerical examples to demonstrate the usefulness of the result with reference to a rare-earth iron garnet film as the rotator.
Development of a hardware-based AC microgrid for AC stability assessment
NASA Astrophysics Data System (ADS)
Swanson, Robert R.
As more power electronic-based devices enable the development of high-bandwidth AC microgrids, the topic of microgrid power distribution stability has become of increased interest. Recently, researchers have proposed a relatively straightforward method to assess the stability of AC systems based upon the time-constants of sources, the net bus capacitance, and the rate limits of sources. In this research, a focus has been to develop a hardware test system to evaluate AC system stability. As a first step, a time domain model of a two converter microgrid was established in which a three phase inverter acts as a power source and an active rectifier serves as an adjustable constant power AC load. The constant power load can be utilized to create rapid power flow transients to the generating system. As a second step, the inverter and active rectifier were designed using a Smart Power Module IGBT for switching and an embedded microcontroller as a processor for algorithm implementation. The inverter and active rectifier were designed to operate simultaneously using a synchronization signal to ensure each respective local controller operates in a common reference frame. Finally, the physical system was created and initial testing performed to validate the hardware functionality as a variable amplitude and variable frequency AC system.
ac response of thin superconductors in the flux-creep regime
NASA Astrophysics Data System (ADS)
Gurevich, A.; Brandt, E. H.
1997-05-01
We calculate both analytically and numerically the ac susceptibility χ(ω) and the nonlinear electromagnetic response of thin superconductor strips and disks of constant thickness in a perpendicular time-dependent magnetic field Ba(t)=B0cos ωt, taking account of the strong nonlinearity of the voltage-current characteristics below the irreversibility line. We consider integral equations of nonlinear nonlocal flux diffusion for a wide class of thermally activated creep models. It is shown that thin superconductors, despite being fully in the critical state, exhibit a universal Meissner-like electromagnetic response in the dissipative flux-creep regime. The expression for the linear ac susceptibility during flux creep appears to be similar to the susceptibility of Ohmic conductors, but with the relaxation time constant replaced by the time t elapsed after flux creep has started. This result is independent of any material parameter or temperature or dc field. For ωt>>:1, we obtain χ(ω)~-1+pln (qiωt)/(iωt), where p and q are constants. Above a critical ac amplitude B0=Bl, the local response of the electric field becomes nonlinear, and there are two distinctive nonlinear regimes at B0>Bl, where Bl~s(d/a)1/2Bp, Bp is a characteristic field of full flux penetration, s(T,B)=\\|dln j/dln t\\| is the dimensionless flux-creep rate and d and a are the sample thickness and width, respectively. For Bl
Photovoltaic system with improved AC connections and method of making same
Cioffi, Philip Michael; Todorovic, Maja Harfman; Herzog, Michael Scott; Korman, Charles Steven; Doherty, Donald M.; Johnson, Neil Anthony
2018-02-13
An alternating current (AC) harness for a photovoltaic (PV) system includes a wire assembly having a first end and a second end, the wire assembly having a plurality of lead wires, and at least one AC connection module positioned at a location along a length of the wire assembly between the first end and the second end. Further, the at least one AC connection module includes a first connection terminal electrically coupled to the plurality of lead wires of the wire assembly and constructed to electrically couple the wire assembly with an output of a first PV module of the PV system. The at least one AC connection module also includes a second connection terminal electrically coupled to the plurality of lead wires of the wire assembly and constructed to electrically couple the wire assembly with an output of a second PV module of the PV system.
AC orbit bump method of local impedance measurement
DOE Office of Scientific and Technical Information (OSTI.GOV)
Smaluk, Victor; Yang, Xi; Blednykh, Alexei
A fast and precise technique of local impedance measurement has been developed and tested at NSLS-II. This technique is based on in-phase sine-wave (AC) excitation of four fast correctors adjacent to the vacuum chamber section, impedance of which is measured. The beam position is measured using synchronous detection. Use of the narrow-band sine-wave signal allows us to improve significantly the accuracy of the orbit bump method. Beam excitation by fast correctors results in elimination of the systematic error caused by hysteresis effect. The systematic error caused by orbit drift is also eliminated because the measured signal is not affected bymore » the orbit motion outside the excitation frequency range. In this article, the measurement technique is described and the result of proof-of-principle experiment carried out at NSLS-II is presented.« less
AC orbit bump method of local impedance measurement
Smaluk, Victor; Yang, Xi; Blednykh, Alexei; ...
2017-08-04
A fast and precise technique of local impedance measurement has been developed and tested at NSLS-II. This technique is based on in-phase sine-wave (AC) excitation of four fast correctors adjacent to the vacuum chamber section, impedance of which is measured. The beam position is measured using synchronous detection. Use of the narrow-band sine-wave signal allows us to improve significantly the accuracy of the orbit bump method. Beam excitation by fast correctors results in elimination of the systematic error caused by hysteresis effect. The systematic error caused by orbit drift is also eliminated because the measured signal is not affected bymore » the orbit motion outside the excitation frequency range. In this article, the measurement technique is described and the result of proof-of-principle experiment carried out at NSLS-II is presented.« less
NASA Astrophysics Data System (ADS)
Dolez, Patricia
Le travail de recherche effectue dans le cadre de ce projet de doctorat a permis la mise au point d'une methode de mesure des pertes ac destinee a l'etude des supraconducteurs a haute temperature critique. Pour le choix des principes de cette methode, nous nous sommes inspires de travaux anterieurs realises sur les supraconducteurs conventionnels, afin de proposer une alternative a la technique electrique, presentant lors du debut de cette these des problemes lies a la variation du resultat des mesures selon la position des contacts de tension sur la surface de l'echantillon, et de pouvoir mesurer les pertes ac dans des conditions simulant la realite des futures applications industrielles des rubans supraconducteurs: en particulier, cette methode utilise la technique calorimetrique, associee a une calibration simultanee et in situ. La validite de la methode a ete verifiee de maniere theorique et experimentale: d'une part, des mesures ont ete realisees sur des echantillons de Bi-2223 recouverts d'argent ou d'alliage d'argent-or et comparees avec les predictions theoriques donnees par Norris, nous indiquant la nature majoritairement hysteretique des pertes ac dans nos echantillons; d'autre part, une mesure electrique a ete realisee in situ dont les resultats correspondent parfaitement a ceux donnes par notre methode calorimetrique. Par ailleurs, nous avons compare la dependance en courant et en frequence des pertes ac d'un echantillon avant et apres qu'il ait ete endommage. Ces mesures semblent indiquer une relation entre la valeur du coefficient de la loi de puissance modelisant la dependance des pertes avec le courant, et les inhomogeneites longitudinales du courant critique induites par l'endommagement. De plus, la variation en frequence montre qu'au niveau des grosses fractures transverses creees par l'endommagement dans le coeur supraconducteur, le courant se partage localement de maniere a peu pres equivalente entre les quelques grains de matiere
Izquierdo-Garcia, David; Catana, Ciprian
2018-01-01
Synopsis Attenuation correction (AC) is one of the most important challenges in the recently introduced combined positron emission tomography/magnetic resonance imaging (PET/MR) scanners. PET/MR AC (MR-AC) approaches aim to develop methods that allow accurate estimation of the linear attenuation coefficients (LACs) of the tissues and other components located in the PET field of view (FoV). MR-AC methods can be divided into three main categories: segmentation-, atlas- and PET-based. This review aims to provide a comprehensive list of the state of the art MR-AC approaches as well as their pros and cons. The main sources of artifacts such as body-truncation, metallic implants and hardware correction will be presented. Finally, this review will discuss the current status of MR-AC approaches for clinical applications. PMID:26952727
NASA Astrophysics Data System (ADS)
Lan, Chunbo; Tang, Lihua; Harne, Ryan L.
2018-05-01
Nonlinear piezoelectric energy harvester (PEH) has been widely investigated during the past few years. Among the majority of these researches, a pure resistive load is used to evaluate power output. To power conventional electronics in practical application, the alternating current (AC) generated by nonlinear PEH needs to be transformed into a direct current (DC) and rectifying circuits are required to interface the device and electronic load. This paper aims at exploring the critical influences of AC and DC interface circuits on nonlinear PEH. As a representative nonlinear PEH, we fabricate and evaluate a monostable PEH in terms of generated power and useful operating bandwidth when it is connected to AC and DC interface circuits. Firstly, the harmonic balance analysis and equivalent circuit representation method are utilized to tackle the modeling of nonlinear energy harvesters connected to AC and DC interface circuits. The performances of the monostable PEH connected to these interface circuits are then analyzed and compared, focusing on the influences of the varying load, excitation and electromechanical coupling strength on the nonlinear dynamics, bandwidth and harvested power. Subsequently, the behaviors of the monostable PEH with AC and DC interface circuits are verified by experiment. Results indicate that both AC and DC interface circuits have a peculiar influence on the power peak shifting and operational bandwidth of the monostable PEH, which is quite different from that on the linear PEH.
Effect of dc field on ac-loss peak in a commercial Bi:2223/Ag tape
NASA Astrophysics Data System (ADS)
Öztürk, Ali; Düzgün, İbrahim; Çelebi, Selahattin
2017-12-01
Measurements of the ac susceptibility in a commercial Bi:2223/Ag tape for some different ac magnetic field amplitudes, Hac, in the presence of bias magnetic field Hdc directed along Hac are reported. It is found that the peak values of the imaginary component of ac susceptibility χ″max versus Hac trace a valley for the orientation where applied field Ha perpendicular to wide face of the tape total. We note that the observation of the valley depends on various parameters such as field dependence parameter n in the critical current density, in the simple power law expression jc = α(T)/Bn, choice of the bias field Hdc together with selected ac field amplitudes Hac, and dimension and geometry of sample studied. Our calculations based on critical state model with jc = α(1 - T/Tcm)p/Bn using the fitting parameters of n = 0.25, p = 2.2, Tcm = 108 K gives quite good results to compare the experimental and calculated curves.
Strömberg, Mattias; Zardán Gómez de la Torre, Teresa; Nilsson, Mats; Svedlindh, Peter; Strømme, Maria
2014-01-01
Bioassays relying on magnetic read-out using probe-tagged magnetic nanobeads are potential platforms for low-cost biodiagnostic devices for pathogen detection. For optimal assay performance it is crucial to apply an easy, efficient and robust bead-probe conjugation protocol. In this paper, sensitive (1.5 pM) singleplex detection of bacterial DNA sequences is demonstrated in a portable AC susceptometer by a magnetic nanobead-based bioassay principle; the volume-amplified magnetic nanobead detection assay (VAM-NDA). Two bead sizes, 100 and 250 nm, are investigated along with a highly efficient, rapid, robust, and stable conjugation chemistry relying on the avidin–biotin interaction for bead-probe attachment. Avidin-biotin conjugation gives easy control of the number of detection probes per bead; thus allowing for systematic investigation of the impact of varying the detection probe surface coverage upon bead immobilization in rolling circle amplified DNA-coils. The existence of an optimal surface coverage is discussed. Biplex VAM-NDA detection is for the first time demonstrated in the susceptometer: Semi-quantitative results are obtained and it is concluded that the concentration of DNA-coils in the incubation volume is of crucial importance for target quantification. The present findings bring the development of commercial biodiagnostic devices relying on the VAM–NDA further towards implementation in point-of-care and outpatient settings. PMID:24174315
Sarkar, Debasish; Mandal, Kalyan; Mandal, Madhuri
2014-03-01
Here solvo-thermal technique has been used to synthesize hollow-nanospheres of magnetite. We have shown that PVP plays an important role to control the particle size and also helps the particles to take the shape of hollow spheres. Structural analysis was done by XRD measurement and morphological measurements like SEM and TEM were performed to confirm the hollow type spherical particles formation and their shape and sizes were also investigated. The detail ac-dc magnetic measurements give an idea about the application of these nano spheres for hyperthermia therapy and spontaneous dye adsorption properties (Gibbs free energy deltaG0 = -0.526 kJ/mol for Eosin and -1.832 kJ/mol for MB) of these particles indicate its use in dye manufacturing company. Being hollow in structure and magnetic in nature such materials will also be useful in other application fields like in drug delivery, arsenic and heavy metal removal by adsorption technique, magnetic separation etc.
NASA Astrophysics Data System (ADS)
Zhu, Jiangong; Sun, Zechang; Wei, Xuezhe; Dai, Haifeng; Gu, Weijun
2017-11-01
Effect of the AC (alternating current) pulse heating method on battery SoH (state of health) for large laminated power lithium-ion batteries at low temperature is investigated experimentally. Firstly, excitation current frequencies, amplitudes, and voltage limitations on cell temperature evolution are studied. High current amplitudes facilitate the heat accumulation and temperature rise. Low frequency region serves as a good innovation to heat the battery because of the large impedance. Wide voltage limitations also enjoy better temperature evolution owing to the less current modulation, but the temperature difference originated from various voltage limitations attenuates due to the decrement of impedance resulting from the temperature rise. Experiments with the thermocouple-embedded cell manifest good temperature homogeneity between the battery surface and interior during the AC heating process. Secondly, the cell capacity, Direct Current resistance and Electrochemical Impedance Spectroscopy are all calibrated to assess the battery SoH after the hundreds of AC pulse heating cycles. Also, all cells are disassembled to investigate the battery internal morphology with the employment of Scanning Electron Microscope and Energy-Dispersive x-ray Spectroscopy techniques. The results indicate that the AC heating method does not aggravate the cell degradation even in the low frequency range (0.5 Hz) under the normal voltage protection limitation.
Plasma Acceleration by Rotating Magnetic Field Method using Helicon Source
NASA Astrophysics Data System (ADS)
Furukawa, Takeru; Shimura, Kaichi; Kuwahara, Daisuke; Shinohara, Shunjiro
2017-10-01
Electrodeless plasma thrusters are very promising due to no electrode damage, leading to realize further deep space exploration. As one of the important proposals, we have been concentrating on Rotating Magnetic Field (RMF) acceleration method. High-dense plasma (up to 1013 cm-3) can be generated by using a radio frequency (rf) external antenna, and also accelerated by an antenna wound around outside of a discharge tube. In this scheme, thrust increment is achieved by the axial Lorentz force caused by non linear effects. RMF penetration condition into plasma can be more satisfied than our previous experiment, by increasing RMF coil current and decreasing the RMF frequency, causing higher thrust and fuel efficiency. Measurements of AC RMF component s have been conducted to investigate the acceleration mechanism and the field penetration experimentally. This study has been partially supported by Grant-in-Aid for Scientific Research (B: 17H02995) from the Japan Society for the Promotion of Science.
Superconducting shielded core reactor with reduced AC losses
Cha, Yung S.; Hull, John R.
2006-04-04
A superconducting shielded core reactor (SSCR) operates as a passive device for limiting excessive AC current in a circuit operating at a high power level under a fault condition such as shorting. The SSCR includes a ferromagnetic core which may be either closed or open (with an air gap) and extends into and through a superconducting tube or superconducting rings arranged in a stacked array. First and second series connected copper coils each disposed about a portion of the iron core are connected to the circuit to be protected and are respectively wound inside and outside of the superconducting tube or rings. A large impedance is inserted into the circuit by the core when the shielding capability of the superconducting arrangement is exceeded by the applied magnetic field generated by the two coils under a fault condition to limit the AC current in the circuit. The proposed SSCR also affords reduced AC loss compared to conventional SSCRs under continuous normal operation.
Study of AC Magnetic Properties and Core Losses of Fe/Fe3O4-epoxy Resin Soft Magnetic Composite
NASA Astrophysics Data System (ADS)
Laxminarayana, T. A.; Manna, Subhendu Kumar; Fernandes, B. G.; Venkataramani, N.
Soft Magnetic Composites (SMC) were prepared by coating of nanocrystalline Fe3O4 particles, synthesized by co-precipitation method, on atomized iron powder of particle size less than 53 μm in size using epoxy resin as a binder between iron and Fe3O4. Fe3O4 was chosen, for its high electric resistivity and suitable magnetic properties, to keep the coating layer magnetic and seek improvement to the magnetic properties of SMC. SEM images and XRD patterns were recorded in order to investigate the coatings on the surface of iron powder. A toroid was prepared by cold compaction of coated iron powder at 1050 MPa and subsequently cured at 150˚C for 1 hr in argon atmosphere. For comparison of properties, a toroid of uncoated iron powder was also compacted at 1050 MPa and annealed at 600˚C for 2 hr in argon atmosphere. The coated iron powder composite has a resistivity of greater than 200 μΩm, measured by four probe method. A comparison of Magnetic Hysteresis loops and core losses using B-H Loop tracer in the frequency range 0 to 1500 Hz on the coated and uncoated iron powder is reported.
Anatomy of the chiral magnetic effect in and out of equilibrium
DOE Office of Scientific and Technical Information (OSTI.GOV)
Kharzeev, Dmitri; Stephanov, Mikhail; Yee, Ho-Ung
Here, we identify a new contribution to the chiral magnetic conductivity at finite frequencies—the magnetization current. This allows us to quantitatively reproduce the known field-theoretic time-dependent (AC) chiral magnetic response in terms of kinetic theory. We also evaluate the corresponding AC chiral magnetic conductivity in two-flavor QCD plasma at weak coupling. The magnetization current results from the spin response of chiral quasiparticles to magnetic field, and is thus proportional to the quasiparticle’s g -factor. Furthemrore, in condensed matter systems, where the chiral quasiparticles are emergent and the g -factor can significantly differ from 2, this opens up the possibility ofmore » tuning the AC chiral magnetic response.« less
Anatomy of the chiral magnetic effect in and out of equilibrium
Kharzeev, Dmitri; Stephanov, Mikhail; Yee, Ho-Ung
2017-03-28
Here, we identify a new contribution to the chiral magnetic conductivity at finite frequencies—the magnetization current. This allows us to quantitatively reproduce the known field-theoretic time-dependent (AC) chiral magnetic response in terms of kinetic theory. We also evaluate the corresponding AC chiral magnetic conductivity in two-flavor QCD plasma at weak coupling. The magnetization current results from the spin response of chiral quasiparticles to magnetic field, and is thus proportional to the quasiparticle’s g -factor. Furthemrore, in condensed matter systems, where the chiral quasiparticles are emergent and the g -factor can significantly differ from 2, this opens up the possibility ofmore » tuning the AC chiral magnetic response.« less
Effect of alignment of easy axes on dynamic magnetization of immobilized magnetic nanoparticles
NASA Astrophysics Data System (ADS)
Yoshida, Takashi; Matsugi, Yuki; Tsujimura, Naotaka; Sasayama, Teruyoshi; Enpuku, Keiji; Viereck, Thilo; Schilling, Meinhard; Ludwig, Frank
2017-04-01
In some biomedical applications of magnetic nanoparticles (MNPs), the particles are physically immobilized. In this study, we explore the effect of the alignment of the magnetic easy axes on the dynamic magnetization of immobilized MNPs under an AC excitation field. We prepared three immobilized MNP samples: (1) a sample in which easy axes are randomly oriented, (2) a parallel-aligned sample in which easy axes are parallel to the AC field, and (3) an orthogonally aligned sample in which easy axes are perpendicular to the AC field. First, we show that the parallel-aligned sample has the largest hysteresis in the magnetization curve and the largest harmonic magnetization spectra, followed by the randomly oriented and orthogonally aligned samples. For example, 1.6-fold increase was observed in the area of the hysteresis loop of the parallel-aligned sample compared to that of the randomly oriented sample. To quantitatively discuss the experimental results, we perform a numerical simulation based on a Fokker-Planck equation, in which probability distributions for the directions of the easy axes are taken into account in simulating the prepared MNP samples. We obtained quantitative agreement between experiment and simulation. These results indicate that the dynamic magnetization of immobilized MNPs is significantly affected by the alignment of the easy axes.
Superconducting magnetic shielding apparatus and method
Clem, John R.; Clem, John R.
1983-01-01
Disclosed is a method and apparatus for providing magnetic shielding around a working volume. The apparatus includes a hollow elongated superconducting shell or cylinder having an elongated low magnetic pinning central portion, and two high magnetic pinning end regions. Transition portions of varying magnetic pinning properties are interposed between the central and end portions. The apparatus further includes a solenoid substantially coextensive with and overlying the superconducting cylinder, so as to be magnetically coupled therewith. The method includes the steps passing a longitudinally directed current through the superconducting cylinder so as to depin magnetic reservoirs trapped in the cylinder. Next, a circumferentially directed current is passed through the cylinder, while a longitudinally directed current is maintained. Depinned magnetic reservoirs are moved to the end portions of the cylinder, where they are trapped.
Superconducting magnetic shielding apparatus and method
Clem, J.R.; Clem, J.R.
1983-10-11
Disclosed are a method and apparatus for providing magnetic shielding around a working volume. The apparatus includes a hollow elongated superconducting shell or cylinder having an elongated low magnetic pinning central portion, and two high magnetic pinning end regions. Transition portions of varying magnetic pinning properties are interposed between the central and end portions. The apparatus further includes a solenoid substantially coextensive with and overlying the superconducting cylinder, so as to be magnetically coupled therewith. The method includes the steps passing a longitudinally directed current through the superconducting cylinder so as to depin magnetic reservoirs trapped in the cylinder. Next, a circumferentially directed current is passed through the cylinder, while a longitudinally directed current is maintained. Depinned magnetic reservoirs are moved to the end portions of the cylinder, where they are trapped. 5 figs.
Superconducting magnetic shielding apparatus and method
Clem, J.R.
1982-07-09
Disclosed is a method and apparatus for providing magnetic shielding around a working volume. The apparatus includes a hollow elongated superconducting shell or cylinder having an elongated low magnetic pinning central portion, and two high magnetic pinning end regions. Transition portions of varying magnetic pinning properties are interposed between the central and end portions. The apparatus further includes a solenoid substantially coextensive with and overlying the superconducting cylinder, so as to be magnetically coupled therewith. The method includes the steps passing a longitudinally directed current through the superconducting cylinder so as to depin magnetic reservoirs trapped in the cylinder. Next, a circumferentially directed current is passed through the cylinder, while a longitudinally directed current is maintained. Depinned magnetic reservoirs are moved to the end portions of the cylinder, where they are trapped.
Magnetic nanoparticle thermometry independent of Brownian relaxation
NASA Astrophysics Data System (ADS)
Zhong, Jing; Schilling, Meinhard; Ludwig, Frank
2018-01-01
An improved method of magnetic nanoparticle (MNP) thermometry is proposed. The phase lag ϕ of the fundamental f 0 harmonic is measured to eliminate the influence of Brownian relaxation on the ratio of 3f 0 to f 0 harmonic amplitudes applying a phenomenological model, thus allowing measurements in high-frequency ac magnetic fields. The model is verified by simulations of the Fokker-Planck equation. An MNP spectrometer is calibrated for the measurements of the phase lag ϕ and the amplitudes of 3f 0 and f 0 harmonics. Calibration curves of the harmonic ratio and tanϕ are measured by varying the frequency (from 10 Hz to 1840 Hz) of ac magnetic fields with different amplitudes (from 3.60 mT to 4.00 mT) at a known temperature. A phenomenological model is employed to fit the calibration curves. Afterwards, the improved method is proposed to iteratively compensate the measured harmonic ratio with tanϕ, and consequently calculate temperature applying the static Langevin function. Experimental results on SHP-25 MNPs show that the proposed method significantly improves the systematic error to 2 K at maximum with a relative accuracy of about 0.63%. This demonstrates the feasibility of the proposed method for MNP thermometry with SHP-25 MNPs even if the MNP signal is affected by Brownian relaxation.
AC losses and stability on large cable-in-conduit superconductors
NASA Astrophysics Data System (ADS)
Bruzzone, Pierluigi
1998-12-01
The cable-in-conduit superconductors are preferred for applications where the AC losses and stability are a major concern, e.g., fusion magnets and SMES. A review of coupling currents loss results for both NbTi and Nb 3Sn cable-in-conduit conductors (CICC) is presented and the AC loss relevant features are listed, with special emphasis for the role of the interstrand resistance and strand coating. The transient stability approach for CICCs is discussed and the analytical models are quoted as well as the relevant experimental database. The likely spectrum of transient disturbance in CICC is reviewed and the need to account for interstrand current sharing in the design is outlined. Eventually a practical criterion for the interstrand resistance is proposed to link the stability and AC loss design.
Spectroscopic Determination of the AC Voltammetric Response.
1984-01-06
characterization of electrode processes. More recently, with the advent of linear sweep cyclic AC voltanmetry(12’ 13), it has been shown that AC methods...implemented with the same instrumentation ( 7 ) as previously used in MSRS and retains both the qualitative and quantitative utility of linear sweep ...voltammetric response (eg. peak width at balf-height, peak separation and cross-over potential in cyclic AC voltametry ) apply equally well to the SACRS
Study on AC loss measurements of HTS power cable for standardizing
NASA Astrophysics Data System (ADS)
Mukoyama, Shinichi; Amemiya, Naoyuki; Watanabe, Kazuo; Iijima, Yasuhiro; Mido, Nobuhiro; Masuda, Takao; Morimura, Toshiya; Oya, Masayoshi; Nakano, Tetsutaro; Yamamoto, Kiyoshi
2017-09-01
High-temperature superconducting power cables (HTS cables) have been developed for more than 20 years. In addition of the cable developments, the test methods of the HTS cables have been discussed and proposed in many laboratories and companies. Recently the test methods of the HTS cables is required to standardize and to common in the world. CIGRE made the working group (B1-31) for the discussion of the test methods of the HTS cables as a power cable, and published the recommendation of the test method. Additionally, IEC TC20 submitted the New Work Item Proposal (NP) based on the recommendation of CIGRE this year, IEC TC20 and IEC TC90 started the standardization work on Testing of HTS AC cables. However, the individual test method that used to measure a performance of HTS cables hasn’t been established as world’s common methods. The AC loss is one of the most important properties to disseminate low loss and economical efficient HTS cables in the world. We regard to establish the method of the AC loss measurements in rational and in high accuracy. Japan is at a leading position in the AC loss study, because Japanese researchers have studied on the AC loss technically and scientifically, and also developed the effective technologies for the AC loss reduction. The JP domestic commission of TC90 made a working team to discussion the methods of the AC loss measurements for aiming an international standard finally. This paper reports about the AC loss measurement of two type of the HTS conductors, such as a HTS conductor without a HTS shield and a HTS conductor with a HTS shield. The AC loss measurement method is suggested by the electrical method..
Frequency-dependent tACS modulation of BOLD signal during rhythmic visual stimulation.
Chai, Yuhui; Sheng, Jingwei; Bandettini, Peter A; Gao, Jia-Hong
2018-05-01
Transcranial alternating current stimulation (tACS) has emerged as a promising tool for modulating cortical oscillations. In previous electroencephalogram (EEG) studies, tACS has been found to modulate brain oscillatory activity in a frequency-specific manner. However, the spatial distribution and hemodynamic response for this modulation remains poorly understood. Functional magnetic resonance imaging (fMRI) has the advantage of measuring neuronal activity in regions not only below the tACS electrodes but also across the whole brain with high spatial resolution. Here, we measured fMRI signal while applying tACS to modulate rhythmic visual activity. During fMRI acquisition, tACS at different frequencies (4, 8, 16, and 32 Hz) was applied along with visual flicker stimulation at 8 and 16 Hz. We analyzed the blood-oxygen-level-dependent (BOLD) signal difference between tACS-ON vs tACS-OFF, and different frequency combinations (e.g., 4 Hz tACS, 8 Hz flicker vs 8 Hz tACS, 8 Hz flicker). We observed significant tACS modulation effects on BOLD responses when the tACS frequency matched the visual flicker frequency or the second harmonic frequency. The main effects were predominantly seen in regions that were activated by the visual task and targeted by the tACS current distribution. These findings bridge different scientific domains of tACS research and demonstrate that fMRI could localize the tACS effect on stimulus-induced brain rhythms, which could lead to a new approach for understanding the high-level cognitive process shaped by the ongoing oscillatory signal. © 2018 Wiley Periodicals, Inc.
Intrinsic resonances and AC-dipole simulations of 3He in the AGS Booster
DOE Office of Scientific and Technical Information (OSTI.GOV)
Hock, Kiel; Meot, Francois; Huang, Haixin
Polarized 3He collisions are part of future RHIC physics programs and of the eRHIC project. The anomalous magnetic moment of 3He (G=-4.184) is roughly three times greater than that of protons (G=1.793), a polarized species that is already used at the Collider-Accelerator complex at BNL. Because of the higher anomolous magnetic moment and possibly injecting into the AGS at rigidities beyond 7 T • m, 3He may have to cross depolarizing intrinsic resonances while accelerating in the Booster. To overcome these strong intrinsic resonances we look to an AC-dipole, which will need to be installed in the Booster. An AC-dipolemore » is a magnet that induces large betatron oscillations which forces the entire bunch to experience a stronger resonance and induce a spin flip of all particles. An artificial intrinsic resonance is created, with close proximity to the original intrinsic resonance, which requires simulations to gauge what magnet strength is required. Simulations have been performed using zgoubi regarding the resonances 0 + v y, 12 - v y, and 6 + v y and show that the AC-dipole is effective at overcoming these resonances. Benefits of avoiding the 0 + v y and crossing the 12 - v y and 6 + v y in the Booster presents the advantage of allowing injection above the 0 + v y in the AGS and minimizes the orbit distortions from the snakes.« less
An ac initiation system is described which uses three ac transmission signals interlocked for safety by frequency, phase, and power discrimination...The ac initiation system is pre-armed by the application of two ac signals have the proper phases, and activates a load when an ac power signal of the proper frequency and power level is applied. (Author)
ERIC Educational Resources Information Center
Arndt, Ebe
2006-01-01
Two recent articles in this journal described how an air core solenoid connected to an ac power source may restore the magnetization of a bar magnet with an alternating magnetic field (see Figs. 1 and 2). Although we are quite accustomed to using a constant magnetic field in an air core solenoid to remagnetize a ferromagnet, it is puzzling that we…
Superconducting magnet and fabrication method
NASA Technical Reports Server (NTRS)
Israelsson, Ulf E. (Inventor); Strayer, Donald M. (Inventor)
1994-01-01
A method of trapping a field in a block of superconductor material, includes providing (i) a block of material defining a bore, (ii) a high permeability core within the bore that defines a low reluctance path through the bore, (iii) a high permeability external structure on the exterior of the block of material that defines a low reluctance path between opposite ends of the core, and (iv) an electromagnet configured to apply a magnetic field around the high permeability core. The method proceeds by energizing the electromagnet to produce an applied magnetic field around the high permeability core, cooling the block of material sufficiently to render the block of material superconducting, de-energizing the electromagnet to result in a trapped magnetic field, and at least partially removing the low reluctance path defined by the core and the external structure in order to increase the magnetic flux density of the trapped magnetic field.
Oddy, M H; Santiago, J G
2004-01-01
We have developed a method for measuring the electrophoretic mobility of submicrometer, fluorescently labeled particles and the electroosmotic mobility of a microchannel. We derive explicit expressions for the unknown electrophoretic and the electroosmotic mobilities as a function of particle displacements resulting from alternating current (AC) and direct current (DC) applied electric fields. Images of particle displacements are captured using an epifluorescent microscope and a CCD camera. A custom image-processing code was developed to determine image streak lengths associated with AC measurements, and a custom particle tracking velocimetry (PTV) code was devised to determine DC particle displacements. Statistical analysis was applied to relate mobility estimates to measured particle displacement distributions.
Method of making permanent magnets
McCallum, R. William; Dennis, Kevin W.; Lograsso, Barbara K.; Anderson, Iver E.
1993-09-07
A method for making an isotropic permanent magnet comprises atomizing a melt of a rare earth-transition metal alloy (e.g., an Nd--Fe--B alloy enriched in Nd and B) under conditions to produce protectively coated, rapidly solidified, generally spherical alloy particles wherein a majority of the particles are produced/size classified within a given size fraction (e.g., 5 to 40 microns diameter) exhibiting optimum as-atomized magnetic properties and subjecting the particles to concurrent elevated temperature and elevated isotropic pressure for a time effective to yield a densified, magnetically isotropic magnet compact having enhanced magnetic properties and mechanical properties.
NASA Astrophysics Data System (ADS)
Pimentel, B.; Caraballo-Vivas, R. J.; Checca, N. R.; Zverev, V. I.; Salakhova, R. T.; Makarova, L. A.; Pyatakov, A. P.; Perov, N. S.; Tishin, A. M.; Shtil, A. A.; Rossi, A. L.; Reis, M. S.
2018-04-01
La0.75Sr0.25MnO3 nanoparticles with average diameter close to 20.9 nm were synthesized using a sol-gel method. Measurements showed that the heating process stops at the blocking temperaturesignificantly below the Curie temperature. Measurements of Specific Absorption Rate (SAR) as a function of AC magnetic field revealed a superquadratic power law, indicating that, in addition to usual Néel and Brown relaxation, the hysteresis also plays an important role in the mechanism of heating. The ability to control the threshold heating temperature, a low remanent magnetization and a low field needed to achieve the magnetic saturation are the advantages of this material for therapeutic magnetic hyperthermia.
Slow magnetic relaxation in a cobalt magnetic chain.
Yang, Chen-I; Chuang, Po-Hsiang; Lu, Kuang-Lieh
2011-04-21
A homospin ladder-like chain, [Co(Hdhq)(OAc)](n) (1; H(2)dhq = 2,3-dihydroxyquinoxaline), shows a single-chain-magnet-like (SCM-like) behavior with the characteristics of frequency dependence of the out-of-phase component in alternating current (ac) magnetic susceptibilities and hysteresis loops. © The Royal Society of Chemistry 2011
Development of AC impedance methods for evaluating corroding metal surfaces and coatings
NASA Technical Reports Server (NTRS)
Knockemus, Ward
1986-01-01
In an effort to investigate metal surface corrosion and the breakdown of metal protective coatings the AC Impedance Method was applied to zinc chromate primer coated 2219-T87 aluminum. The model 368-1 AC Impedance Measurement System recently acquired by the MSFC Corrosion Research Branch was used to monitor changing properties of coated aluminum disks immersed in 3.5% NaCl buffered at ph 5.5 over three to four weeks. The DC polarization resistance runs were performed on the same samples. The corrosion system can be represented by an electronic analog called an equivalent circuit that consists of transistors and capacitors in specific arrangements. This equivalent circuit parallels the impedance behavior of the corrosion system during a frequency scan. Values for resistances and capacities that can be assigned in the equivalent circuit following a least squares analysis of the data describe changes that occur on the corroding metal surface and in the protective coating. A suitable equivalent circuit was determined that predicts the correct Bode phase and magnitude for the experimental sample. The DC corrosion current density data are related to equivalent circuit element parameters.
Method of Menu Selection by Gaze Movement Using AC EOG Signals
NASA Astrophysics Data System (ADS)
Kanoh, Shin'ichiro; Futami, Ryoko; Yoshinobu, Tatsuo; Hoshimiya, Nozomu
A method to detect the direction and the distance of voluntary eye gaze movement from EOG (electrooculogram) signals was proposed and tested. In this method, AC-amplified vertical and horizontal transient EOG signals were classified into 8-class directions and 2-class distances of voluntary eye gaze movements. A horizontal and a vertical EOGs during eye gaze movement at each sampling time were treated as a two-dimensional vector, and the center of gravity of the sample vectors whose norms were more than 80% of the maximum norm was used as a feature vector to be classified. By the classification using the k-nearest neighbor algorithm, it was shown that the averaged correct detection rates on each subject were 98.9%, 98.7%, 94.4%, respectively. This method can avoid strict EOG-based eye tracking which requires DC amplification of very small signal. It would be useful to develop robust human interfacing systems based on menu selection for severely paralyzed patients.
Nonstationary behavior of a high-spin molecule in a bifrequency alternating current magnetic field
NASA Astrophysics Data System (ADS)
Tokman, I. D.; Vugalter, G. A.
2002-07-01
An interaction of a high-spin molecule with a bifrequency ac magnetic field, occurring at times much shorter than the molecule relaxation times, has been considered. The molecule is subjected to a dc magnetic field perpendicular to the easy anisotropy axis of the molecule. The bifrequency ac field is a superposition of two ac fields, one of which is perpendicular to the easy anisotropy axis and causes resonant transitions between the lower states of the fundamental and first excited doublets. The other ac field is parallel to the easy anisotropy axis and has a frequency much smaller than the frequency of the first ac field. It has been shown that, first, the molecule can absorb or emit energy, depending on the frequency of the low-frequency ac field, second, the bifrequency ac magnetic field induces tunneling of the molecule magnetization with the Rabi frequency. The conditions of observation of the effects predicted are discussed.
Liu, Haiyi; Sun, Jianfei; Wang, Haoyao; Wang, Peng; Song, Lina; Li, Yang; Chen, Bo; Zhang, Yu; Gu, Ning
2015-06-08
A kinetics-based method is proposed to quantitatively characterize the collective magnetization of colloidal magnetic nanoparticles. The method is based on the relationship between the magnetic force on a colloidal droplet and the movement of the droplet under a gradient magnetic field. Through computational analysis of the kinetic parameters, such as displacement, velocity, and acceleration, the magnetization of colloidal magnetic nanoparticles can be calculated. In our experiments, the values measured by using our method exhibited a better linear correlation with magnetothermal heating, than those obtained by using a vibrating sample magnetometer and magnetic balance. This finding indicates that this method may be more suitable to evaluate the collective magnetism of colloidal magnetic nanoparticles under low magnetic fields than the commonly used methods. Accurate evaluation of the magnetic properties of colloidal nanoparticles is of great importance for the standardization of magnetic nanomaterials and for their practical application in biomedicine. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
High strength undiffused brushless machine and method
DOE Office of Scientific and Technical Information (OSTI.GOV)
Hsu, John S
2009-04-14
A method and apparatus in which a rotor (11) and a stator (17) define a radial air gap (20) for receiving AC flux and at least one DC excitation coil (23, 24) positioned near the stator end turn to produce DC flux in axial air gaps (21, 22) additive to the AC flux. Side magnets (16) and flux-guiding magnets (14) are provided as boundaries separating the side poles (12a, 12b) of opposite polarity from other portions of the rotor (11) and from each other to define PM poles (12a, 12b) for conveying the DC flux to or from the primarymore » air gap (20) and for inhibiting flux from leaking from said pole portions prior to reaching the primary air gap (20). Side magnets (16), side poles (12a and 12b), flux-guiding magnets (14), ferromagnetic end plates (11c), non-magnetic end plates (12c), and ring bands (37) are optionally provided for performance improvement.« less
Han, Zhantao; Sani, Badruddeen; Akkanen, Jarkko; Abel, Sebastian; Nybom, Inna; Karapanagioti, Hrissi K; Werner, David
2015-04-09
Addition of activated carbon (AC) or biochar (BC) to sediment to reduce the chemical and biological availability of organic contaminants is a promising in-situ remediation technology. But concerns about leaving the adsorbed pollutants in place motivate research into sorbent recovery methods. This study explores the use of magnetic sorbents. A coal-based magnetic activated carbon (MAC) was identified as the strongest of four AC and BC derived magnetic sorbents for polycyclic aromatic hydrocarbons (PAHs) remediation. An 8.1% MAC amendment (w/w, equal to 5% AC content) was found to be as effective as 5% (w/w) pristine AC in reducing aqueous PAHs within three months by 98%. MAC recovery from sediment after three months was 77%, and incomplete MAC recovery had both, positive and negative effects. A slight rebound of aqueous PAH concentrations was observed following the MAC recovery, but aqueous PAH concentrations then dropped again after six months, likely due to the presence of the 23% unrecovered MAC. On the other hand, the 77% recovery of the 8.1% MAC dose was insufficient to reduce ecotoxic effects of fine grained AC or MAC amendment on the egestion rate, growth and reproduction of the AC sensitive species Lumbriculus variegatus. Copyright © 2014 Elsevier B.V. All rights reserved.
AC Electric Field Communication for Human-Area Networking
NASA Astrophysics Data System (ADS)
Kado, Yuichi; Shinagawa, Mitsuru
We have proposed a human-area networking technology that uses the surface of the human body as a data transmission path and uses an AC electric field signal below the resonant frequency of the human body. This technology aims to achieve a “touch and connect” intuitive form of communication by using the electric field signal that propagates along the surface of the human body, while suppressing both the electric field radiating from the human body and mutual interference. To suppress the radiation field, the frequency of the AC signal that excites the transmitter electrode must be lowered, and the sensitivity of the receiver must be raised while reducing transmission power to its minimally required level. We describe how we are developing AC electric field communication technologies to promote the further evolution of a human-area network in support of ubiquitous services, focusing on three main characteristics, enabling-transceiver technique, application-scenario modeling, and communications quality evaluation. Special attention is paid to the relationship between electro-magnetic compatibility evaluation and regulations for extremely low-power radio stations based on Japan's Radio Law.
Method of making permanent magnets
McCallum, R.W.; Dennis, K.W.; Lograsso, B.K.; Anderson, I.E.
1993-09-07
A method for making an isotropic permanent magnet comprises atomizing a melt of a rare earth-transition metal alloy (e.g., an Nd--Fe--B alloy enriched in Nd and B) under conditions to produce protectively coated, rapidly solidified, generally spherical alloy particles. Wherein a majority of the particles are produced/size classified within a given size fraction (e.g., 5 to 40 microns diameter) exhibiting optimum as-atomized magnetic properties and subjecting the particles to concurrent elevated temperature and elevated isotropic pressure for a time effective to yield a densified, magnetically isotropic magnet compact having enhanced magnetic properties and mechanical properties. 13 figures.
Ren, Qinlong
2018-02-10
Efficient pumping of blood flow in a microfluidic device is essential for rapid detection of bacterial bloodstream infections (BSI) using alternating current (AC) electrokinetics. Compared with AC electro-osmosis (ACEO) phenomenon, the advantage of AC electrothermal (ACET) mechanism is its capability of pumping biofluids with high electrical conductivities at a relatively high AC voltage frequency. In the current work, the microfluidic pumping of non-Newtonian blood flow using ACET forces is investigated in detail by modeling its multi-physics process with hybrid boundary element method (BEM) and immersed boundary-lattice Boltzmann method (IB-LBM). The Carreau-Yasuda model is used to simulate the realistic rheological behavior of blood flow. The ACET pumping efficiency of blood flow is studied in terms of different AC voltage magnitudes and frequencies, thermal boundary conditions of electrodes, electrode configurations, channel height, and the channel length per electrode pair. Besides, the effect of rheological behavior on the blood flow velocity is theoretically analyzed by comparing with the Newtonian fluid flow using scaling law analysis under the same physical conditions. The results indicate that the rheological behavior of blood flow and its frequency-dependent dielectric property make the pumping phenomenon of blood flow different from that of the common Newtonian aqueous solutions. It is also demonstrated that using a thermally insulated electrode could enhance the pumping efficiency dramatically. Besides, the results conclude that increasing the AC voltage magnitude is a more economical pumping approach than adding the number of electrodes with the same energy consumption when the Joule heating effect is acceptable. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
NASA Astrophysics Data System (ADS)
Donoso, Guillermo; Ladera, Celso L.
2012-11-01
We study the nonlinear oscillations of a forced and weakly dissipative spring-magnet system moving in the magnetic fields of two fixed coaxial, hollow induction coils. As the first coil is excited with a dc current, both a linear and a cubic magnet-position dependent force appear on the magnet-spring system. The second coil, located below the first, excited with an ac current, provides the oscillating magnetic driving force on the system. From the magnet-coil interactions, we obtain, analytically, the nonlinear motion equation of the system, found to be a forced and damped cubic Duffing oscillator moving in a quartic potential. The relative strengths of the coefficients of the motion equation can be easily set by varying the coils’ dc and ac currents. We demonstrate, theoretically and experimentally, the nonlinear behaviour of this oscillator, including its oscillation modes and nonlinear resonances, the fold-over effect, the hysteresis and amplitude jumps, and its chaotic behaviour. It is an oscillating system suitable for teaching an advanced experiment in nonlinear dynamics both at senior undergraduate and graduate levels.
Methods, systems and apparatus for controlling operation of two alternating current (AC) machines
Gallegos-Lopez, Gabriel [Torrance, CA; Nagashima, James M [Cerritos, CA; Perisic, Milun [Torrance, CA; Hiti, Silva [Redondo Beach, CA
2012-02-14
A system is provided for controlling two AC machines. The system comprises a DC input voltage source that provides a DC input voltage, a voltage boost command control module (VBCCM), a five-phase PWM inverter module coupled to the two AC machines, and a boost converter coupled to the inverter module and the DC input voltage source. The boost converter is designed to supply a new DC input voltage to the inverter module having a value that is greater than or equal to a value of the DC input voltage. The VBCCM generates a boost command signal (BCS) based on modulation indexes from the two AC machines. The BCS controls the boost converter such that the boost converter generates the new DC input voltage in response to the BCS. When the two AC machines require additional voltage that exceeds the DC input voltage required to meet a combined target mechanical power required by the two AC machines, the BCS controls the boost converter to drive the new DC input voltage generated by the boost converter to a value greater than the DC input voltage.
NASA Astrophysics Data System (ADS)
Pandey, R. S.; Singh, Vikrant; Rani, Anju; Varughese, George; Singh, K. M.
2018-05-01
In the present paper Oblique propagating electromagnetic ion-cyclotron wave has been analyzed for anisotropic multi ion plasma (H+, He+, O+ ions) in earth magnetosphere for the Dione shell of L=7 i.e., the outer radiation belt of the magnetosphere for Loss-cone distribution function with a spectral index j in the presence of A.C. electric field. Detail for particle trajectories and dispersion relation has been derived by using the method of characteristic solution on the basis of wave particle interaction and transformation of energy. Results for the growth rate have been calculated numerically for various parameters and have been compared for different ions present in magnetosphere. It has been found that for studying the wave over wider spectrum, anisotropy for different values of j should be taken. The effect of frequency of A.C. electric field and angle which propagation vector make with magnetic field, on growth rate has been explained.
Atomization methods for forming magnet powders
Sellers, Charles H.; Branagan, Daniel J.; Hyde, Timothy A.
2000-01-01
The invention encompasses methods of utilizing atomization, methods for forming magnet powders, methods for forming magnets, and methods for forming bonded magnets. The invention further encompasses methods for simulating atomization conditions. In one aspect, the invention includes an atomization method for forming a magnet powder comprising: a) forming a melt comprising R.sub.2.1 Q.sub.13.9 B.sub.1, Z and X, wherein R is a rare earth element; X is an element selected from the group consisting of carbon, nitrogen, oxygen and mixtures thereof; Q is an element selected from the group consisting of Fe, Co and mixtures thereof; and Z is an element selected from the group consisting of Ti, Zr, Hf and mixtures thereof; b) atomizing the melt to form generally spherical alloy powder granules having an internal structure comprising at least one of a substantially amorphous phase or a substantially nanocrystalline phase; and c) heat treating the alloy powder to increase an energy product of the alloy powder; after the heat treatment, the alloy powder comprising an energy product of at least 10 MGOe. In another aspect, the invention includes a magnet comprising R, Q, B, Z and X, wherein R is a rare earth element; X is an element selected from the group consisting of carbon, nitrogen, oxygen and mixtures thereof; Q is an element selected from the group consisting of Fe, Co and mixtures thereof; and Z is an element selected from the group consisting of Ti, Zr, Hf and mixtures thereof; the magnet comprising an internal structure comprising R.sub.2.1 Q.sub.13.9 B.sub.1.
2013-01-01
Cobalt-nickel (Co-Ni) binary alloy nanowires of different compositions were co-deposited in the nanopores of highly ordered anodic aluminum oxide (AAO) templates from a single sulfate bath using alternating current (AC) electrodeposition. AC electrodeposition was accomplished without modifying or removing the barrier layer. Field emission scanning electron microscope was used to study the morphology of templates and alloy nanowires. Energy-dispersive X-ray analysis confirmed the deposition of Co-Ni alloy nanowires in the AAO templates. Average diameter of the alloy nanowires was approximately 40 nm which is equal to the diameter of nanopore. X-ray diffraction analysis showed that the alloy nanowires consisted of both hexagonal close-packed and face-centered cubic phases. Magnetic measurements showed that the easy x-axis of magnetization is parallel to the nanowires with coercivity of approximately 706 Oe. AC electrodeposition is very simple, fast, and is useful for the homogenous deposition of various secondary nanostuctured materials into the nanopores of AAO. PMID:23941234
Dynamic magnetic hysteresis and nonlinear susceptibility of antiferromagnetic nanoparticles
NASA Astrophysics Data System (ADS)
Kalmykov, Yuri P.; Ouari, Bachir; Titov, Serguey V.
2016-08-01
The nonlinear ac stationary response of antiferromagnetic nanoparticles subjected to both external ac and dc fields of arbitrary strength and orientation is investigated using Brown's continuous diffusion model. The nonlinear complex susceptibility and dynamic magnetic hysteresis (DMH) loops of an individual antiferromagnetic nanoparticle are evaluated and compared with the linear regime for extensive ranges of the anisotropy, the ac and dc magnetic fields, damping, and the specific antiferromagnetic parameter. It is shown that the shape and area of the DMH loops of antiferromagnetic particles are substantially altered by applying a dc field that permits tuning of the specific magnetic power loss in the nanoparticles.
Method and system for an on-chip AC self-test controller
Flanagan, John D [Rhinebeck, NY; Herring, Jay R [Poughkeepsie, NY; Lo, Tin-Chee [Fishkill, NY
2008-09-30
A method and system for performing AC self-test on an integrated circuit that includes a system clock for use during normal operation are provided. The method includes applying a long data capture pulse to a first test register in response to the system clock, applying an at speed data launch pulse to the first test register in response to the system clock, inputting the data from the first register to a logic path in response to applying the at speed data launch pulse to the first test register, applying an at speed data capture pulse to a second test register in response to the system clock, inputting the logic path output to the second test register in response to applying the at speed data capture pulse to the second test register, and applying a long data launch pulse to the second test register in response to the system clock.
Method and system for an on-chip AC self-test controller
Flanagan, John D.; Herring, Jay R.; Lo, Tin-Chee
2006-06-06
A method for performing AC self-test on an integrated circuit, including a system clock for use during normal operation. The method includes applying a long data capture pulse to a first test register in response to the system clock, and further applying at an speed data launch pulse to the first test register in response to the system clock. Inputting the data from the first register to a logic path in response to applying the at speed data launch pulse to the first test register. Applying at speed data capture pulse to a second test register in response to the system clock. Inputting the output from the logic path to the second test register in response to applying the at speed data capture pulse to the second register. Applying a long data launch pulse to the second test register in response to the system clock.
Effect of Cr3+ substitution on AC susceptibility of Ba hexaferrite nanoparticles
NASA Astrophysics Data System (ADS)
Slimani, Y.; Baykal, A.; Manikandan, A.
2018-07-01
In this study, nano-sized particles of BaCrxFe12-xO19 (0.0 ≤ x ≤ 1.0) hexaferrite were fabricated through citrate auto gel combustion process and the impact of Cr-ion substitution on ac magnetic susceptibility properties of Ba-hexaferrite were explored. X-ray powder diffraction (XRD) measurements approved the purity of prepared samples and showed a reduction of the average crystallite size with increasing the content of Cr. Transmission electron microscopy (TEM) observation indicated the hexagonal morphology of all samples. AC susceptibility measurements displayed a frequency dependence of the magnetic responses. These measurements indicated that there are strong magnetic interactions (which is the highest for BaCr0.3Fe11.7O19 NP) between particles which cause a superspin glass-like (SSG) behavior at low temperatures. Estimating the values of loss power density revealed an increase of loss power density with increasing Cr-substitution element. The relative sensitivity of the prepared MNPs to the variation of applied frequency is very influenced by Cr-substitution and is highest in BaCr0.3Fe11.7O19 MNPs, suggesting that this sample can be considered as magnetic nanomaterial for hyperthermia and for many other applications.
NASA Astrophysics Data System (ADS)
Ouari, Bachir; Titov, Serguey V.; El Mrabti, Halim; Kalmykov, Yuri P.
2013-02-01
The nonlinear ac susceptibility and dynamic magnetic hysteresis (DMH) of a single domain ferromagnetic particle with biaxial anisotropy subjected to both external ac and dc fields of arbitrary strength and orientation are treated via Brown's continuous diffusions model [W. F. Brown, Jr., Phys. Rev. 130, 1677 (1963)] of magnetization orientations. The DMH loops and nonlinear ac susceptibility strongly depend on the dc and ac field strengths, the polar angle between the easy axis of the particle, the external field vectors, temperature, and damping. In contrast to uniaxial particles, the nonlinear ac stationary response and DMH strongly depend on the azimuthal direction of the ac field and the biaxiality parameter Δ.
Effects of humidity on the magnetic and woody characteristics of powder-type magnetic wood
NASA Astrophysics Data System (ADS)
Oka, H.; Tokuta, H.; Namizaki, Y.; Sekino, N.
2004-05-01
Among three types of proposed magnetic wood, powder-type magnetic wood can be made of recycled magnetic materials from IT devices, consumer electronics and waste wood. Because of its wood powder content, powder-type magnetic wood shows special characteristics different from those of typical magnetic materials. We focused on the relationship between humidity and magnetic characteristics of powder-type magnetic wood. The magnetic powder ratio, wood powder density and magnetic binder density were all examined as parameters for AC permeability.
3D Magnetization Vector Inversion of Magnetic Data: Improving and Comparing Methods
NASA Astrophysics Data System (ADS)
Liu, Shuang; Hu, Xiangyun; Zhang, Henglei; Geng, Meixia; Zuo, Boxin
2017-12-01
Magnetization vector inversion is an useful approach to invert for magnetic anomaly in the presence of significant remanent magnetization and self-demagnetization. However, magnetizations are usually obtained in many different directions under the influences of geophysical non-uniqueness. We propose an iteration algorithm of magnetization vector inversion (M-IDI) that one couple of magnetization direction is iteratively computed after the magnetization intensity is recovered from the magnitude magnetic anomaly. And we compare it with previous methods of (1) three orthogonal components inversion of total magnetization vector at Cartesian framework (MMM), (2) intensity, inclination and declination inversion at spherical framework (MID), (3) directly recovering the magnetization inclination and declination (M-IDCG) and (4) estimating the magnetization direction using correlation method (M-IDC) at the sequential inversion frameworks. The synthetic examples indicate that MMM returns multiply magnetization directions and MID results are strongly dependent on initial model and parameter weights. M-IDI computes faster than M-IDC and achieves a constant magnetization direction compared with M-IDCG. Additional priori information constraints can improve the results of MMM, MID and M-IDCG. Obtaining one magnetization direction, M-IDC and M-IDI are suitable for single and isolated anomaly. Finally, M-IDI and M-IDC are used to invert and interpret the magnetic anomaly of the Galinge iron-ore deposit (NW China) and the results are verified by information from drillholes and physical properties measurements of ore and rock samples. Magnetization vector inversion provides a comprehensive way to evaluate and investigate the remanent magnetization and self-demagnetization.
Strömberg, Mattias; Zardán Gómez de la Torre, Teresa; Nilsson, Mats; Svedlindh, Peter; Strømme, Maria
2014-01-01
Bioassays relying on magnetic read-out using probe-tagged magnetic nanobeads are potential platforms for low-cost biodiagnostic devices for pathogen detection. For optimal assay performance it is crucial to apply an easy, efficient and robust bead-probe conjugation protocol. In this paper, sensitive (1.5 pM) singleplex detection of bacterial DNA sequences is demonstrated in a portable AC susceptometer by a magnetic nanobead-based bioassay principle; the volume-amplified magnetic nanobead detection assay (VAM-NDA). Two bead sizes, 100 and 250 nm, are investigated along with a highly efficient, rapid, robust, and stable conjugation chemistry relying on the avidin-biotin interaction for bead-probe attachment. Avidin-biotin conjugation gives easy control of the number of detection probes per bead; thus allowing for systematic investigation of the impact of varying the detection probe surface coverage upon bead immobilization in rolling circle amplified DNA-coils. The existence of an optimal surface coverage is discussed. Biplex VAM-NDA detection is for the first time demonstrated in the susceptometer: Semi-quantitative results are obtained and it is concluded that the concentration of DNA-coils in the incubation volume is of crucial importance for target quantification. The present findings bring the development of commercial biodiagnostic devices relying on the VAM-NDA further towards implementation in point-of-care and outpatient settings. © 2013 The Authors. Biotechnology Journal published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. This is an open access article under the terms of the Creative Commons Attribution-License, which permits use and distribution in any medium, provided the original work is properly cited.
Corrosion and protection of NdFeB type magnets
NASA Astrophysics Data System (ADS)
Cavalloti, P.; Bozzini, B.; Cecchini, R.; Bava, G. F.; Davies, H. A.; Hoggarth, C.
1992-02-01
A general mechanism for the corrosion behaviour of NdFeB magnets is presented, related to the magnet heterogeneity with the presence of different phases. Cathodic control is outlined. An electrochemical method to assess the corrosion resistance of magnets, with and without coatings, is proposed; it is based on the study of the transient voltage at the magnet surface after a second cathodic current pulse in a suitable aggressive solution and its dependence on the amount of cathodic current circulating. Suitable pretreatments have been tried and interesting results obtained with passivation pretreatments, giving phosphorous Nd at grain boundaries. Coatings if sintered and plastic magnets have been tried using several methods. Good results are obtained with Zn-Co layers on sintered magnets and a sol-gel glass on powders for plastic magnets. Improved ACS (Autocatalytic Chemical Deposition) Ni=P coatings have been realized, with an alkaline brass flash plating to start ACD deposition.
NASA Astrophysics Data System (ADS)
Yagotintsev, K.; Nijhuis, A.
2018-07-01
Two prototype Nb3Sn cable-in-conduit conductors conductors were designed and manufactured for the toroidal field (TF) magnet system of the envisaged European DEMO fusion reactor. The AC loss, contact resistance and mechanical properties of two sample conductors were tested in the Twente Cryogenic Cable Press under cyclic load up to 30 000 cycles. Though both conductors were designed to operate at 82 kA in a background magnetic field of 13.6 T, they reflect different approaches with respect to the magnet winding pack assembly. The first approach is based on react and wind technology while the second is the more common wind and react technology. Each conductor was tested first for AC loss in virgin condition without handling. The impact of Lorentz load during magnet operation was simulated using the cable press. In the press each conductor specimen was subjected to transverse cyclic load up to 30 000 cycles in liquid helium bath at 4.2 K. Here a summary of results for AC loss, contact resistance, conductor deformation, mechanical heat production and conductor stiffness evolution during cycling of the load is presented. Both conductors showed similar mechanical behaviour but quite different AC loss. In comparison with previously tested ITER TF conductors, both DEMO TF conductors possess very low contact resistance resulting in high coupling loss. At the same time, load cycling has limited impact on properties of DEMO TF conductors in comparison with ITER TF conductors.
Durrett, Timothy; Ohlrogge, John; Pollard, Michael
2016-05-03
The present invention relates to novel diacylglycerol acyltransferase genes and proteins, and methods of their use. In particular, the invention describes genes encoding proteins having diacylglycerol acetyltransferase activity, specifically for transferring an acetyl group to a diacylglycerol substrate to form acetyl-Triacylglycerols (ac-TAGS), for example, a 3-acetyl-1,2-diacyl-sn-glycerol. The present invention encompasses both native and recombinant wild-type forms of the transferase, as well as mutants and variant forms. The present invention also relates to methods of using novel diacylglycerol acyltransferase genes and proteins, including their expression in transgenic organisms at commercially viable levels, for increasing production of 3-acetyl-1,2-diacyl-sn-glycerols in plant oils and altering the composition of oils produced by microorganisms, such as yeast, by increasing ac-TAG production. Additionally, oils produced by methods of the present inventions comprising genes and proteins are contemplated for use as biodiesel fuel, in polymer production and as naturally produced food oils with reduced calories.
Simulation of the AC corona phenomenon with experimental validation
NASA Astrophysics Data System (ADS)
Villa, Andrea; Barbieri, Luca; Marco, Gondola; Malgesini, Roberto; Leon-Garzon, Andres R.
2017-11-01
The corona effect, and in particular the Trichel phenomenon, is an important aspect of plasma physics with many technical applications, such as pollution reduction, surface and medical treatments. This phenomenon is also associated with components used in the power industry where it is, in many cases, the source of electro-magnetic disturbance, noise and production of undesired chemically active species. Despite the power industry to date using mainly alternating current (AC) transmission, most of the studies related to the corona effect have been carried out with direct current (DC) sources. Therefore, there is technical interest in validating numerical codes capable of simulating the AC phenomenon. In this work we describe a set of partial differential equations that are comprehensive enough to reproduce the distinctive features of the corona in an AC regime. The model embeds some selectable chemical databases, comprising tens of chemical species and hundreds of reactions, the thermal dynamics of neutral species and photoionization. A large set of parameters—deduced from experiments and numerical estimations—are compared, to assess the effectiveness of the proposed approach.
Investigation of the transition of multicycle AC operation in ISTTOK under edge electrode biasing
NASA Astrophysics Data System (ADS)
Malaquias, A.; Henriques, R. B.; Silva, C.; Figueiredo, H.; Nedzelskiy, I. S.; Fernandes, H.; Sharma, R.; Plyusnin, V. V.
2017-11-01
In this paper we present recent results obtained on plasma edge electrode biasing during AC discharges. The goal is to obtain experimental evidence on a number of plasma parameters that can play a role during the AC transition on the repeatability and reproducibility of AC operation. The control of the plasma density in the quiescent phase is made just before the AC transition by means of positive edge biasing leading to a transitory improved of density (30%-40%). Gas puff experiments show that the increase of background gas pressure during discharge led to a better success of the AC transition. The experimental results indicate that the increase of density during the AC transition induced by edge biasing is followed by an electron temperature drop. The drop in electron temperature leads in most cases the formation of runaway electrons. It has been observed that the runaway population during discharge flattop depends on the interplay between gas content and plasma density and temperature. The results also confirm that the correct balance of external magnetic fields is crucial during the AC transition phase where drift electron currents are formed. The results from the heavy ion beam diagnostic show that the formation of plasma current during consecutive AC transitions is asymmetric. Numerical simulations indicate that for some particular conditions this result could be reproduced from assuming the presence of two counter-currents during AC transition.
Structural investigation of chemically synthesized ferrite magnetic nanomaterials
NASA Astrophysics Data System (ADS)
Uyanga, E.; Sangaa, D.; Hirazawa, H.; Tsogbadrakh, N.; Jargalan, N.; Bobrikov, I. A.; Balagurov, A. M.
2018-05-01
In recent times, interest in ferrite magnetic nanomaterials has considerably grown, mainly due to their highly promising medical and biological applications. Spinel ferrite powder samples, with high heat generation abilities in AC magnetic fields, were studied for their application to the hyperthermia treatment of cancer tumors. These properties of ferrites strongly depend on their chemical composition, ion distribution between crystallographic positions, magnetic structure and method of preparation. In this study, crystal and magnetic structures of several magnetic spinels were investigated by neutron diffraction. The explanation of the mechanism triggering the heat generation ability in the magnetic materials, and the electronic and magnetic states of ferrite-spinel type structures, were theoretically defined by a first-principles method. Ferrites with the composition of CuxMg1-xFe2O4 have been investigated as a heat generating magnetic nanomaterial. Atomic fraction of copper in ferrite was varied between 0 and 100% (that is, x between 0 and 1.0 with 0.2 steps), with the copper dope limit corresponding to appear a tetragonal phase.
Ammonia synthesis using magnetic induction method (MIM)
NASA Astrophysics Data System (ADS)
Puspitasari, P.; Razak, J. Abd; Yahya, N.
2012-09-01
The most challenging issues for ammonia synthesis is to get the high yield. New approach of ammonia synthesis by using Magnetic Induction Method (MIM) and the Helmholtz Coils has been proposed. The ammonia detection was done by using Kjeldahl Method and FTIR. The system was designed by using Autocad software. The magnetic field of MIM was vary from 100mT-200mT and the magnetic field for the Helmholtz coils was 14mT. The FTIR result shows that ammonia has been successfully formed at stretching peaks 1097,1119,1162,1236, 1377, and 1464 cm-1. UV-VIS result shows the ammonia bond at 195nm of wavelength. The ammonia yield was increase to 244.72μmole/g.h by using the MIM and six pairs of Helmholtz coils. Therefore this new method will be a new promising method to achieve the high yield ammonia at ambient condition (at 25δC and 1atm), under the Magnetic Induction Method (MIM).
Powell, J.; Reich, M.; Danby, G.
1997-07-22
A magnetic imager includes a generator for practicing a method of applying a background magnetic field over a concealed object, with the object being effective to locally perturb the background field. The imager also includes a sensor for measuring perturbations of the background field to detect the object. In one embodiment, the background field is applied quasi-statically. And, the magnitude or rate of change of the perturbations may be measured for determining location, size, and/or condition of the object. 25 figs.
Methods, systems and apparatus for controlling operation of two alternating current (AC) machines
Gallegos-Lopez, Gabriel [Torrance, CA; Nagashima, James M [Cerritos, CA; Perisic, Milun [Torrance, CA; Hiti, Silva [Redondo Beach, CA
2012-06-05
A system is provided for controlling two alternating current (AC) machines via a five-phase PWM inverter module. The system comprises a first control loop, a second control loop, and a current command adjustment module. The current command adjustment module operates in conjunction with the first control loop and the second control loop to continuously adjust current command signals that control the first AC machine and the second AC machine such that they share the input voltage available to them without compromising the target mechanical output power of either machine. This way, even when the phase voltage available to either one of the machines decreases, that machine outputs its target mechanical output power.
2006-01-01
1 AC -130 Employment Subject Area Aviation EWS 2006 Author Captain Robert Hornick, USMC Report Documentation Page Form ApprovedOMB No. 0704...00-2006 4. TITLE AND SUBTITLE AC -130 Employment 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER... AC -130 gunship is an aircraft that can provide all of these needs. Regrettably, there are too few AC -130’s in the inventory to cover all the needs
Bacterially synthesized ferrite nanoparticles for magnetic hyperthermia applications.
Céspedes, Eva; Byrne, James M; Farrow, Neil; Moise, Sandhya; Coker, Victoria S; Bencsik, Martin; Lloyd, Jonathan R; Telling, Neil D
2014-11-07
Magnetic hyperthermia uses AC stimulation of magnetic nanoparticles to generate heat for cancer cell destruction. Whilst nanoparticles produced inside magnetotactic bacteria have shown amongst the highest reported heating to date, these particles are magnetically blocked so that strong heating occurs only for mobile particles, unless magnetic field parameters are far outside clinical limits. Here, nanoparticles extracellularly produced by the bacteria Geobacter sulfurreducens are investigated that contain Co or Zn dopants to tune the magnetic anisotropy, saturation magnetization and nanoparticle sizes, enabling heating within clinical field constraints. The heating mechanisms specific to either Co or Zn doping are determined from frequency dependent specific absorption rate (SAR) measurements and innovative AC susceptometry simulations that use a realistic model concerning clusters of polydisperse nanoparticles in suspension. Whilst both particle types undergo magnetization relaxation and show heating effects in water under low AC frequency and field, only Zn doped particles maintain relaxation combined with hysteresis losses even when immobilized. This magnetic heating process could prove important in the biological environment where nanoparticle mobility may not be possible. Obtained SARs are discussed regarding clinical conditions which, together with their enhanced MRI contrast, indicate that biogenic Zn doped particles are promising for combined diagnostics and cancer therapy.
NASA Astrophysics Data System (ADS)
Nayek, C.; Manna, K.; Imam, A. A.; Alqasrawi, A. Y.; Obaidat, I. M.
2018-02-01
Understanding the size dependent magnetic anisotropy of iron oxide nanoparticles is essential for the successful application of these nanoparticles in several technological and medical fields. PEG-coated iron oxide (Fe3O4) nanoparticles with core diameters of 12 nm, 15 nm, and 16 nm were synthesized by the usual co-precipitation method. The morphology and structure of the nanoparticles were investigated using transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD). Magnetic measurements were conducted using a SQUID. The effective magnetic anisotropy was calculated using two methods from the magnetization measurements. In the first method the zero-field-cooled magnetization versus temperature measurements were used at several applied magnetic fields. In the second method we used the temperature-dependent coercivity curves obtained from the zero-field-cooled magnetization versus magnetic field hysteresis loops. The role of the applied magnetic field on the effective magnetic anisotropy, calculated form the zero-field-cooled magnetization versus temperature measurements, was revealed. The size dependence of the effective magnetic anisotropy constant Keff obtained by the two methods are compared and discussed.
Powell, James; Reich, Morris; Danby, Gordon
1997-07-22
A magnetic imager 10 includes a generator 18 for practicing a method of applying a background magnetic field over a concealed object, with the object being effective to locally perturb the background field. The imager 10 also includes a sensor 20 for measuring perturbations of the background field to detect the object. In one embodiment, the background field is applied quasi-statically. And, the magnitude or rate of change of the perturbations may be measured for determining location, size, and/or condition of the object.
NASA Astrophysics Data System (ADS)
Palihawadana-Arachchige, Maheshika; Nemala, Humeshkar; Naik, Vaman M.; Naik, Ratna
2017-01-01
Magnetic hyperthermia (MHT), where localized heating is generated when magnetic nanoparticles (MNPs) are subjected to a radiofrequency magnetic field, has a great potential as a non-invasive cancer therapy treatment. The efficiency of heat generation depends on the magnetic properties of MNPs, such as saturation magnetization (Ms) and magnetic anisotropy (K), as well as the particle size distribution and magnetic dipolar interactions. We have investigated MHT in two Fe3O4 ferrofluids prepared by co-precipitation (CP) and hydrothermal (HT) synthesis methods showing similar physical particle size distribution (14 ± 4 nm) and saturation magnetization (70 ± 2 emu/g of Fe3O4) but very different specific absorption rates (SAR) of ˜110 W/g and ˜40 W/g at room temperature (measured with an ac magnetic field amplitude of 240 Oe and a frequency of 375 kHz). This observed reduction in SAR has been explained by taking into account the dipolar interactions and the distribution of the magnetic core size of MNPs in ferrofluids. The HT ferrofluid shows a higher effective dipolar interaction and a wider distribution of the magnetic core size of MNPs compared to those of the CP ferrofluid. We have fitted the temperature dependent SAR data using the linear response theory, incorporating an effective dipolar interaction, to determine the magnetic anisotropy constant of MNPs prepared by CP (22 ± 2 kJ/m3) and HT (26 ± 2 kJ/m3) synthesis methods. These values are in good agreement with the magnetic anisotropy constant determined using frequency and temperature dependent magnetic susceptibility data obtained on powder samples.
Method for regenerating magnetic polyamine-epichlorohydrin resin
Kochen, Robert L.; Navratil, James D.
1997-07-29
Magnetic polymer resins capable of efficient removal of actinides and heavy metals from contaminated water are disclosed together with methods for making, using, and regenerating them. The resins comprise polyamine-epichlorohydrin resin beads with ferrites attached to the surfaces of the beads. Markedly improved water decontamination is demonstrated using these magnetic polymer resins of the invention in the presence of a magnetic field, as compared with water decontamination methods employing ordinary ion exchange resins or ferrites taken separately.
Nikolo, Martin; Singleton, John; Zapf, Vivien S.; ...
2016-07-20
The de-pinning or irreversibility lines were determined by ac susceptibility, magnetization, radio-frequency proximity detector oscillator (PDO), and resistivity methods in Ba(Fe 0.92Co 0.08) 2As 2 ( T c = 23.2 K), Ba(Fe 0.95Ni 0.05) 2As 2 ( T c = 20.4 K), and Ba(Fe 0.94Ni 0.06) 2As 2 ( T c = 18.5 K) bulk superconductors in ac, dc, and pulsed magnetic fields up to 65 T. A new method of extracting the irreversibility fields from the radio-frequency proximity detector oscillator induction technique is described. Wide temperature broadening of the irreversibility lines, for any given combination of ac and dcmore » fields, is dependent on the time frame of measurement. Increasing the magnetic field sweep rate (dH/dt) shifts the irreversibility lines to higher temperatures up to about dH/d t = 40,000 Oe/s; for higher dH/dt, there is little impact on the irreversibility line. There is an excellent data match between the irreversibility fields obtained from magnetization hysteresis loops, PDO, and ac susceptibility measurements, but not from resistivity measurements in these materials. Lower critical field vs. temperature phase diagrams are measured. Their very low values near 0 T indicate that these materials are in mixed state in nonzero magnetic fields, and yet the strength of the vortex pinning enables very high irreversibility fields, as high as 51 T at 1.5 K for the Ba(Fe 0.92Co 0.08) 2As 2 polycrystalline sample, showing a promise for liquid helium temperature applications.« less
NASA Astrophysics Data System (ADS)
Boutami, R.; Borge, M. J. G.; Mach, H.; Kurcewicz, W.; Fraile, L. M.; Gulda, K.; Aas, A. J.; García-Raffi, L. M.; Løvhøiden, G.; Martínez, T.; Rubio, B.; Taín, J. L.; Tengblad, O.
2008-10-01
The low-energy structure of 231Ac has been investigated by means of γ ray spectroscopy following the β decay of 231Ra. Multipolarities of 28 transitions have been established by measuring conversion electrons with a MINI-ORANGE electron spectrometer. The decay scheme of 231Ra → 231Ac has been constructed for the first time. The Advanced Time Delayed βγγ(t) method has been used to measure the half-lives of five levels. The moderately fast B(E1) transition rates derived suggest that the octupole effects, albeit weak, are still present in this exotic nucleus.
Magnetic adsorbents for the removal of Hg (II) and phenanthrene from aqueous solutions
NASA Astrophysics Data System (ADS)
Isari, Ekavi; Karapanagioti, Hrissi K.; Manariotis, Ioannis D.; Werner, David
2015-04-01
Activated carbon (AC) acts as a strong binding agent that lowers the pollutant concentration and, thus its toxicity. Another promising sorbent material in environmental applications is biochar (BC) which is obtained from the incomplete combustion of carbon-rich biomass under oxygen-limited conditions. Both of these materials could be used as soil or sediment amendments that would lower the toxicity in the aqueous phase. A draw back of this technique is that although the pollutant will remain non- bioavailable for many years being sorbed into these sorbents, it actually stays into the system. The objective of this study was (a) to synthesize a magnetic powdered activated carbon (AC/Fe) and magnetic powdered biochar (BC/Fe) produced from commercial AC1 and AC2 samples and biochar respectively and (b) to evaluate the potential use of AC/Fe and BIO/Fe to remove aqueous Hg (II) or phenanthrene while being magnetically recoverable. The BC was produced from olive pomace. The surface area, the pore volume, and the average pore size of each sorbent were determined using gas (N2) adsorption-desorption cycles and the Brunauer, Emmett, and Teller (BET) equation. Isotherms with 30 adsorption and 20 desorption points were conducted at liquid nitrogen temperature (77K). Open surface area and micropore volume were determined using t-plot method and Harkins & Jura equation. For both AC/Fe, surface area measurements resulted in 66% those of corresponding AC. For BC/Fe, the surface area was 82% that of BC. Batch experiments with all sorbent samples and mercury solutions were conducted at room temperature (25oC) and at pH 5 in order to compare the sorption properties of the materials. Similar tests were performed with phenanthrene solutions. Based on mercury isotherm data, AC/Fe and BC/Fe are effective sorbents but with lower sorption capacity compared to the initial materials (50-75% lower). All these properties point to promising materials that can effectively be used for in
Methods for characterizing magnetic footprints of perpendicular magnetic recording writer heads
Li, Shaoping; Lin, Ed; George, Zach; Terrill, Dave; Mendez, H.; Santucci, J.; Yie, Derek
2014-01-01
In this work, the magnetic footprints, along with some of its dynamic features in recording process, of perpendicular magnetic recording writer heads have been characterized by using three different techniques. Those techniques are the spin-stand stationary footprint technique, the spin-stand dynamic footprint technique, and the coherent writing technique combined with magnetic force microscope imaging method. The characteristics of those techniques have been compared to one another. It was found experimentally that the spin-stand stationary method could not precisely catch some peculiar recording dynamics of the write heads in certain conditions. The advantages and disadvantages among all those techniques are also examined and discussed in detail. PMID:24753633
Absolute method of measuring magnetic susceptibility
Thorpe, A.; Senftle, F.E.
1959-01-01
An absolute method of standardization and measurement of the magnetic susceptibility of small samples is presented which can be applied to most techniques based on the Faraday method. The fact that the susceptibility is a function of the area under the curve of sample displacement versus distance of the magnet from the sample, offers a simple method of measuring the susceptibility without recourse to a standard sample. Typical results on a few substances are compared with reported values, and an error of less than 2% can be achieved. ?? 1959 The American Institute of Physics.
Hidden transition in multiferroic and magnetodielectric CuCrO2 evidenced by ac-susceptibility
NASA Astrophysics Data System (ADS)
Shukla, Kaushak K.; Pal, Arkadeb; Singh, Abhishek; Singh, Rahul; Saha, J.; Sinha, A. K.; Ghosh, A. K.; Patnaik, S.; Awasthi, A. M.; Chatterjee, Sandip
2017-04-01
Ferroelectric polarization, magnetic-field dependence of the dielectric constant and ac and dc magnetizations of frustrated CuCrO2 have been measured. A new spin freezing transition below 32 K is observed which is thermally driven. The nature of the spin freezing is to be a single-ion process. Dilution by the replacements of Cr ions by magnetic Mn ions showed suppression of the spin freezing transition suggesting it to be fundamentally a single-ion freezing process. The observed freezing, which is seemingly associated to geometrical spin frustration, represents a novel form of magnetic glassy behavior.
Third harmonic ac susceptibility of superconductors with finite thickness
NASA Astrophysics Data System (ADS)
Qin, M. J.; Ong, C. K.
Third harmonic ac susceptibility of superconducting strips with finite thickness in perpendicularly applied magnetic field Ha = H0 sin(ω t) have been calculated. The flux creep effect is taken into account by using a power-law electric field E( j) = Ec( j/ jc) n. Results for different thicknesses and creep exponents n have been derived and compared to the results derived from the Bean critical state model.
Method for regenerating magnetic polyamine-epichlorohydrin resin
Kochen, R.L.; Navratil, J.D.
1997-07-29
Magnetic polymer resins capable of efficient removal of actinides and heavy metals from contaminated water are disclosed together with methods for making, using, and regenerating them. The resins comprise polyamine-epichlorohydrin resin beads with ferrites attached to the surfaces of the beads. Markedly improved water decontamination is demonstrated using these magnetic polymer resins of the invention in the presence of a magnetic field, as compared with water decontamination methods employing ordinary ion exchange resins or ferrites taken separately. 9 figs.
Mathematical model for the dc-ac inverter for the Space Shuttle
NASA Technical Reports Server (NTRS)
Berry, Frederick C.
1987-01-01
The reader is informed of what was done for the mathematical modeling of the dc-ac inverter for the Space Shuttle. The mathematical modeling of the dc-ac inverter is an essential element in the modeling of the electrical power distribution system of the Space Shuttle. The electrical power distribution system which is present on the Space Shuttle is made up to 3 strings each having a fuel cell which provides dc to those systems which require dc, and the inverters which convert the dc to ac for those elements which require ac. The inverters are units which are 2 wire structures for the main dc inputs and 2 wire structures for the ac output. When 3 are connected together a 4 wire wye connection results on the ac side. The method of modeling is performed by using a Least Squares curve fitting method. A computer program is presented for implementation of the model along with graphs and tables to demonstrate the accuracy of the model.
NASA Astrophysics Data System (ADS)
Pryadun, Vladimir
2005-03-01
Rectification of AC current has been observed in plain superconducting Nb films and in Nb/Ni films with symmetric periodic pinning centers. The rectified DC voltage appears for various sample geometries (cross or strip) both along and transverse to the alternating current direction, is nearly anti-symmetric with perpendicular magnetic field and strongly dependent on temperature below Tc. Analyses of the data at different temperatures, drive frequencies from 100kHz to 150MHz and at the different sample sides [1] shows that not far below Tc the rectification phenomena can be understood in terms of generation of electric fields due to local excess of critical current. Further below Tc anisotropic pinning effects could also contribute to the rectification. [1] F.G.Aliev, et al., Cond. Mat.405656. Supported by Comunidad Autonoma de Madrid -CAM/07N/0050/2002
AC Loss Analysis of MgB2-Based Fully Superconducting Machines
NASA Astrophysics Data System (ADS)
Feddersen, M.; Haran, K. S.; Berg, F.
2017-12-01
Superconducting electric machines have shown potential for significant increase in power density, making them attractive for size and weight sensitive applications such as offshore wind generation, marine propulsion, and hybrid-electric aircraft propulsion. Superconductors exhibit no loss under dc conditions, though ac current and field produce considerable losses due to hysteresis, eddy currents, and coupling mechanisms. For this reason, many present machines are designed to be partially superconducting, meaning that the dc field components are superconducting while the ac armature coils are conventional conductors. Fully superconducting designs can provide increases in power density with significantly higher armature current; however, a good estimate of ac losses is required to determine the feasibility under the machines intended operating conditions. This paper aims to characterize the expected losses in a fully superconducting machine targeted towards aircraft, based on an actively-shielded, partially superconducting machine from prior work. Various factors are examined such as magnet strength, operating frequency, and machine load to produce a model for the loss in the superconducting components of the machine. This model is then used to optimize the design of the machine for minimal ac loss while maximizing power density. Important observations from the study are discussed.
Superconducting magnetic energy storage for asynchronous electrical systems
Boenig, Heinrich J.
1986-01-01
A superconducting magnetic energy storage coil connected in parallel between converters of two or more ac power systems provides load leveling and stability improvement to any or all of the ac systems. Control is provided to direct the charging and independently the discharging of the superconducting coil to at least a selected one of the ac power systems.
Magnetic suspension and balance system study
NASA Technical Reports Server (NTRS)
Boom, R. W.; Eyssa, Y. M.; Mcintosh, G. E.; Abdelsalam, M. K.
1984-01-01
A compact design for a superconducting magnetic suspension and balance system is developed for a 8 ft. x 8 ft. transonic wind tunnel. The main features of the design are: a compact superconducting solenoid in the suspended airplane model; permanent magnet wings; one common liquid helium dewar for all superconducting coils; efficient new race track coils for roll torques; use of established 11 kA cryostable AC conductor; acceptable AC losses during 10 Hz control even with all steel structure; and a 560 liter/hour helium liquefier. Considerable design simplicity, reduced magnet weights, and reduced heat leak results from using one common dewar which eliminates most heavy steel structure between coils and the suspended model. Operational availability is thought to approach 100% for such magnet systems. The weight and cost of the magnet system is approximately one-third that of previous less compact designs.
Measurement of internal defects in aluminum using a nano-granular in-gap magnetic sensor
NASA Astrophysics Data System (ADS)
Ozawa, T.; Yabukami, S.; Totsuka, J.; Koyama, S.; Hayasaka, J.; Wako, N.; Arai, K. I.
2015-05-01
Techniques for identifying defects in metals are very important in a wide variety of manufacturing areas. The present paper reports an eddy current testing method that employs a nano-granular in-gap magnetic sensor (GIGS) to detect internal defects in aluminum boards. The GIGS consists of a tunnel magnetoresistive film with nanometer sized grains and two yokes. In the presence of an external magnetic field, the nano-granular film exhibits only a small change in resistance due to the tunnel magnetoresistive effect. However, by placing it between two yokes, the magnetic flux can be greatly concentrated, thus increasing the change in resistance. The GIGS is a magnetic-field sensor that exploits this principle to achieve enhanced sensitivity. Moreover, because it has a cross-sectional yolk area of just 80 μm × 0.5 μm, it achieves outstanding spatial resolution. In the present study, it is used in combination with an eddy-current method in order to detect internal defects in aluminum. In this method, an excitation coil is used to apply an AC magnetic field perpendicular to the aluminum surface. This induces eddy currents in the metal, which in turn give rise to an AC magnetic field, which is then measured by the GIGS. The presence of defects in the aluminum distorts the eddy current flow, causing a change in the magnitude and distribution of the magnetic field. Such changes can be detected using the GIGS. In the present study, the proposed method was used to successfully detect indentations with diameters of 5 mm on the rear surface of an aluminum plate.
A new method to determine magnetic properties of the unsaturated-magnetized rotor of a novel gyro
NASA Astrophysics Data System (ADS)
Li, Hai; Liu, Xiaowei; Dong, Changchun; Zhang, Haifeng
2016-06-01
A new method is proposed to determine magnetic properties of the unsaturated-magnetized, small and irregular shaped rotor of a novel gyro. The method is based on finite-element analysis and the measurements of the magnetic flux density distribution, determining magnetic parameters by comparing the magnetic flux intensity distribution differences between the modeling results under different parameters and the measured ones. Experiment on a N30 Grade NdFeB magnet shows that its residual magnetic flux density is 1.10±0.01 T, and coercive field strength is 801±3 kA/m, which are consistent with the given parameters of the material. The method was applied to determine the magnetic properties of the rotor of the gyro, and the magnetic properties acquired were used to predict the open-loop gyro precession frequency. The predicted precession frequency should be larger than 12.9 Hz, which is close to the experimental result 13.5 Hz. The result proves that the method is accurate in estimating the magnetic properties of the rotor of the gyro.
A dynamic method for magnetic torque measurement
NASA Technical Reports Server (NTRS)
Lin, C. E.; Jou, H. L.
1994-01-01
In a magnetic suspension system, accurate force measurement will result in better control performance in the test section, especially when a wider range of operation is required. Although many useful methods were developed to obtain the desired model, however, significant error is inevitable since the magnetic field distribution of the large-gap magnetic suspension system is extremely nonlinear. This paper proposed an easy approach to measure the magnetic torque of a magnetic suspension system using an angular photo encoder. Through the measurement of the velocity change data, the magnetic torque is converted. The proposed idea is described and implemented to obtain the desired data. It is useful to the calculation of a magnetic force in the magnetic suspension system.
Magnetic method for stimulating transport in fluids
Martin, James E.; Solis, Kyle J.
2016-10-18
A method for producing mass and heat transport in fluids, wherein the method does not rely on conventional convection, that is, it does not require gravity, a thermal gradient, or a magnetic field gradient. This method gives rise to a unique class of vigorous, field-controllable flow patterns termed advection lattices. The advection lattices can be used to transport heat and/or mass in any desired direction using only magnetic fields.
Fan, Bingfei; Li, Qingguo; Wang, Chao; Liu, Tao
2017-01-01
Magnetic and inertial sensors have been widely used to estimate the orientation of human segments due to their low cost, compact size and light weight. However, the accuracy of the estimated orientation is easily affected by external factors, especially when the sensor is used in an environment with magnetic disturbances. In this paper, we propose an adaptive method to improve the accuracy of orientation estimations in the presence of magnetic disturbances. The method is based on existing gradient descent algorithms, and it is performed prior to sensor fusion algorithms. The proposed method includes stationary state detection and magnetic disturbance severity determination. The stationary state detection makes this method immune to magnetic disturbances in stationary state, while the magnetic disturbance severity determination helps to determine the credibility of magnetometer data under dynamic conditions, so as to mitigate the negative effect of the magnetic disturbances. The proposed method was validated through experiments performed on a customized three-axis instrumented gimbal with known orientations. The error of the proposed method and the original gradient descent algorithms were calculated and compared. Experimental results demonstrate that in stationary state, the proposed method is completely immune to magnetic disturbances, and in dynamic conditions, the error caused by magnetic disturbance is reduced by 51.2% compared with original MIMU gradient descent algorithm. PMID:28534858
Sreenivasulu, Gollapudi; Qu, Peng; Petrov, Vladimir; Qu, Hongwei; Srinivasan, Gopalan
2016-02-20
Multiferroic composites with ferromagnetic and ferroelectric phases have been studied in recent years for use as sensors of AC and DC magnetic fields. Their operation is based on magneto-electric (ME) coupling between the electric and magnetic subsystems and is mediated by mechanical strain. Such sensors for AC magnetic fields require a bias magnetic field to achieve pT-sensitivity. Novel magnetic sensors with a permanent magnet proof mass, either on a ferroelectric bimorph or a ferromagnetic-ferroelectric composite, are discussed. In both types, the interaction between the applied AC magnetic field and remnant magnetization of the magnet results in a mechanical strain and a voltage response in the ferroelectric. Our studies have been performed on sensors with a Nd-Fe-B permanent magnet proof mass on (i) a bimorph of oppositely-poled lead zirconate titanate (PZT) platelets and (ii) a layered multiferroic composite of PZT-Metglas-Ni. The sensors have been characterized in terms of sensitivity and equivalent magnetic noise N. Noise N in both type of sensors is on the order of 200 pT/√Hz at 1 Hz, a factor of 10 improvement compared to multiferroic sensors without a proof mass. When the AC magnetic field is applied at the bending resonance for the bimorph, the measured N ≈ 700 pT/√Hz. We discuss models based on magneto-electro-mechanical coupling at low frequency and bending resonance in the sensors and theoretical estimates of ME voltage coefficients are in very good agreement with the data.
Sreenivasulu, Gollapudi; Qu, Peng; Petrov, Vladimir; Qu, Hongwei; Srinivasan, Gopalan
2016-01-01
Multiferroic composites with ferromagnetic and ferroelectric phases have been studied in recent years for use as sensors of AC and DC magnetic fields. Their operation is based on magneto-electric (ME) coupling between the electric and magnetic subsystems and is mediated by mechanical strain. Such sensors for AC magnetic fields require a bias magnetic field to achieve pT-sensitivity. Novel magnetic sensors with a permanent magnet proof mass, either on a ferroelectric bimorph or a ferromagnetic-ferroelectric composite, are discussed. In both types, the interaction between the applied AC magnetic field and remnant magnetization of the magnet results in a mechanical strain and a voltage response in the ferroelectric. Our studies have been performed on sensors with a Nd-Fe-B permanent magnet proof mass on (i) a bimorph of oppositely-poled lead zirconate titanate (PZT) platelets and (ii) a layered multiferroic composite of PZT-Metglas-Ni. The sensors have been characterized in terms of sensitivity and equivalent magnetic noise N. Noise N in both type of sensors is on the order of 200 pT/√Hz at 1 Hz, a factor of 10 improvement compared to multiferroic sensors without a proof mass. When the AC magnetic field is applied at the bending resonance for the bimorph, the measured N ≈ 700 pT/√Hz. We discuss models based on magneto-electro-mechanical coupling at low frequency and bending resonance in the sensors and theoretical estimates of ME voltage coefficients are in very good agreement with the data. PMID:26907290
DOE Office of Scientific and Technical Information (OSTI.GOV)
Chen, Z.; Hering, P.; Brown, S. B.
To study the rapid evolution of AC conductivity from ultrafast laser excited warm dense matter (WDM), a spatial chirp single-shot method is developed utilizing a crossing angle pump-probe configuration. The pump beam is shaped individually in two spatial dimensions so that it can provide both sufficient laser intensity to excite the material to warm dense matter state and a uniform time window of up to 1 ps with sub-100 fs FWHM temporal resolution. Here, temporal evolution of AC conductivity in laser excited warm dense gold was also measured.
Chen, Z.; Hering, P.; Brown, S. B.; ...
2016-09-19
To study the rapid evolution of AC conductivity from ultrafast laser excited warm dense matter (WDM), a spatial chirp single-shot method is developed utilizing a crossing angle pump-probe configuration. The pump beam is shaped individually in two spatial dimensions so that it can provide both sufficient laser intensity to excite the material to warm dense matter state and a uniform time window of up to 1 ps with sub-100 fs FWHM temporal resolution. Here, temporal evolution of AC conductivity in laser excited warm dense gold was also measured.
Successful enrichment of the ubiquitous freshwater acI Actinobacteria.
Garcia, Sarahi L; McMahon, Katherine D; Grossart, Hans-Peter; Warnecke, Falk
2014-02-01
Actinobacteria of the acI lineage are often the numerically dominant bacterial phylum in surface freshwaters, where they can account for > 50% of total bacteria. Despite their abundance, there are no described isolates. In an effort to obtain enrichment of these ubiquitous freshwater Actinobacteria, diluted freshwater samples from Lake Grosse Fuchskuhle, Germany, were incubated in 96-well culture plates. With this method, a successful enrichment containing high abundances of a member of the lineage acI was established. Phylogenetic classification showed that the acI Actinobacteria of the enrichment belonged to the acI-B2 tribe, which seems to prefer acidic lakes. This enrichment grows to low cell densities and thus the oligotrophic nature of acI-B2 was confirmed. © 2013 Society for Applied Microbiology and John Wiley & Sons Ltd.
Research and simulation of the decoupling transformation in AC motor vector control
NASA Astrophysics Data System (ADS)
He, Jiaojiao; Zhao, Zhongjie; Liu, Ken; Zhang, Yongping; Yao, Tuozhong
2018-04-01
Permanent magnet synchronous motor (PMSM) is a nonlinear, strong coupling, multivariable complex object, and transformation decoupling can solve the coupling problem of permanent magnet synchronous motor. This paper gives a permanent magnet synchronous motor (PMSM) mathematical model, introduces the permanent magnet synchronous motor vector control coordinate transformation in the process of modal matrix inductance matrix transform through the matrix related knowledge of different coordinates of diagonalization, which makes the coupling between the independent, realize the control of motor current and excitation the torque current coupling separation, and derived the coordinate transformation matrix, the thought to solve the coupling problem of AC motor. Finally, in the Matlab/Simulink environment, through the establishment and combination between the PMSM ontology, coordinate conversion module, built the simulation model of permanent magnet synchronous motor vector control, introduces the model of each part, and analyzed the simulation results.
Method for using magnetic particles in droplet microfluidics
NASA Technical Reports Server (NTRS)
Shah, Gaurav Jitendra (Inventor); Kim, Chang-Jin (Inventor)
2012-01-01
Methods of utilizing magnetic particles or beads (MBs) in droplet-based (or digital) microfluidics are disclosed. The methods may be used in enrichment or separation processes. A first method employs the droplet meniscus to assist in the magnetic collection and positioning of MBs during droplet microfluidic operations. The sweeping movement of the meniscus lifts the MBs off the solid surface and frees them from various surface forces acting on the MBs. A second method uses chemical additives to reduce the adhesion of MBs to surfaces. Both methods allow the MBs on a solid surface to be effectively moved by magnetic force. Droplets may be driven by various methods or techniques including, for example, electrowetting, electrostatic, electromechanical, electrophoretic, dielectrophoretic, electroosmotic, thermocapillary, surface acoustic, and pressure.
Magnetic Control in Crystal Growth from a Melt
NASA Astrophysics Data System (ADS)
Huang, Yue
Control of bulk melt crystal growth techniques is desirable for producing semiconductors with the highest purity and ternary alloys with tunable electrical properties. Because these molten materials are electrically conducting, external magnetic fields are often employed to regulate the flow in the melt. However, complicated by the coupled flow, thermal, electromagnetic and chemical physics, such magnetic control is typically empirical or even an educated guess. Two magnetic flow control mechanisms: flow damping by steady magnetic fields, and flow stirring by alternating magnetic fields, are investigated numerically. Magnetic damping during optically-heated float-zone crystal growth is modeled using a spectral collocation method. The Marangoni convection at the free melt-gas interface is suppressed when exposed to a steady axial magnetic field, measured by the Hartmann number Ha. As a result, detrimental flow instabilities are suppressed, and an almost quiescent region forms in the interior, ideal for single crystal growth. Using normal mode linear stability analyses, dominant flow instabilities are determined in a range applicable to experiments (up to Ha = 300 for Pr = 0.02, and up to Ha = 500 for Pr = 0.001). The hydrodynamic nature of the instability for small Prandtl number Pr liquid bridges is confirmed by energy analyses. Magnetic stirring is modeled for melt crystal growth in an ampule exposed to a transverse rotating magnetic field. Decoupled from the flow field at small magnetic Reynolds number, the electromagnetic field is first solved via finite element analysis. The flow field is then solved using the spectral element method. At low to moderate AC frequencies (up to a few kHz), the electromagnetic body force is dominant in the azimuthal direction, which stirs a steady axisymmetric flow primarily in the azimuthal direction. A weaker secondary flow develops in the meridional plane. However, at high AC frequencies (on the order of 10 kHz and higher), only
NASA Astrophysics Data System (ADS)
Khan, Sajid; Yazdani-Kachoei, M.; Jalali-Asadabadi, S.; Ahmad, Iftikhar
2017-12-01
In this paper, we explore the structural and magnetic properties as well as electric field gradient (EFG), hyperfine field (HFF) and quadrupole coupling constant in actinide digallide AcGa2 (Ac = U, Np, Pu) using LDA, GGA, LDA+U, GGA+U and hybrid functional with Wu-Cohen Generalized Gradient approximation HF-WC. Relativistic effects of the electrons are considered by including spin-orbit coupling. The comparison of the calculated structural parameters and magnetic properties with the available experimental results confirms the consistency and hence effectiveness of our theoretical tools. The calculated magnetic moments demonstrate that UGa2 and NpGa2 are ferromagnetic while PuGa2 is antiferromagnetic in nature. The EFG of AcGa2 is reported for the first time. The HFF, EFG and quadrupole coupling constant in AcGa2 (Ac = U, Np, Pu) are mainly originated from f-f and p-p contributions of Ac atom and p-p contribution of Ga atom.
NASA Astrophysics Data System (ADS)
Tadyszak, Krzysztof; Kertmen, Ahmet; Coy, Emerson; Andruszkiewicz, Ryszard; Milewski, Sławomir; Kardava, Irakli; Scheibe, Błażej; Jurga, Stefan; Chybczyńska, Katarzyna
2017-07-01
Superparamagnetic behavior in aqueously well dispersible magnetite core-shell Fe3O4@SiO2 nanoparticles is presented. The magnetic properties of core-shell nanoparticles were measured with use of the DC, AC magnetometry and EPR spectroscopy. Particles where characterized by HR-TEM and Raman spectroscopy, showing a crystalline magnetic core of 11.5 ± 0.12 nm and an amorphous silica shell of 22 ± 1.5 nm in thickness. The DC, AC magnetic measurements confirmed the superparamagnetic nature of nanoparticles, additionally the EPR studies performed at much higher frequency than DC, AC magnetometry (9 GHz) have confirmed the paramagnetic nature of the nanoparticles. Our results show the excellent magnetic behavior of the particles with a clear magnetite structure, which are desirable properties for environmental remediation and biomedical applications.
Fock, Jeppe; Parmvi, Mattias; Strömberg, Mattias; Svedlindh, Peter; Donolato, Marco; Hansen, Mikkel Fougt
2017-02-15
There is an increasing need to develop biosensor methods that are highly sensitive and that can be combined with low-cost consumables. The use of magnetic nanoparticles (MNPs) is attractive because their detection is compatible with low-cost disposables and because application of a magnetic field can be used to accelerate assay kinetics. We present the first study and comparison of the performance of magnetic susceptibility measurements and a newly proposed optomagnetic method. For the comparison we use the C-reactive protein (CRP) induced agglutination of identical samples of 100nm MNPs conjugated with CRP antibodies. Both methods detect agglutination as a shift to lower frequencies in measurements of the dynamics in response to an applied oscillating magnetic field. The magnetic susceptibility method probes the magnetic response whereas the optomagnetic technique probes the modulation of laser light transmitted through the sample. The two techniques provided highly correlated results upon agglutination when they measure the decrease of the signal from the individual MNPs (turn-off detection strategy), whereas the techniques provided different results, strongly depending on the read-out frequency, when detecting the signal due to MNP agglomerates (turn-on detection strategy). These observations are considered to be caused by differences in the volume-dependence of the magnetic and optical signals from agglomerates. The highest signal from agglomerates was found in the optomagnetic signal at low frequencies. Copyright © 2016 Elsevier B.V. All rights reserved.
Harmonic phases of the nanoparticle magnetization: An intrinsic temperature probe
NASA Astrophysics Data System (ADS)
Garaio, Eneko; Collantes, Juan-Mari; Garcia, Jose Angel; Plazaola, Fernando; Sandre, Olivier
2015-09-01
Magnetic fluid hyperthermia is a promising cancer therapy in which magnetic nanoparticles act as heat sources activated by an external AC magnetic field. The nanoparticles, located near or inside the tumor, absorb energy from the magnetic field and then heat up the cancerous tissues. During the hyperthermia treatment, it is crucial to control the temperature of different tissues: too high temperature can cause undesired damage in healthy tissues through an uncontrolled necrosis. However, the current thermometry in magnetic hyperthermia presents some important technical problems. The widely used optical fiber thermometers only provide the temperature in a discrete set of spatial points. Moreover, surgery is required to locate these probes in the correct place. In this scope, we propose here a method to measure the temperature of a magnetic sample. The approach relies on the intrinsic properties of the magnetic nanoparticles because it is based on monitoring the thermal dependence of the high order harmonic phases of the nanoparticle dynamic magnetization. The method is non-invasive and it does not need any additional probe or sensor attached to the magnetic nanoparticles. Moreover, this method has the potential to be used together with the magnetic particle imaging technique to map the spatial distribution of the temperature.
Kim, Dong-Hyun; Kim, Kyoung-Nam; Kim, Kwang-Mahn; Lee, Yong-Keun
2009-01-01
The delivery of hyperthermic thermoseeds to a specific target site with minimal side effects is an important challenge in targeted hyperthermia, which employs magnetic method and functional polymers. An external magnetic field is used to control the site-specific targeting of the magnetic nanoparticles. Polymer-coated magnetic nanoparticles can confer a higher affinity to the biological cell membranes. In this study, uncoated, chitosan-coated, and starch-coated magnetic nanoparticles were synthesized for use as a hyperthermic thermoseed. Each sample was examined with respect to their applications to hyperthermia using XRD, VSM, and FTIR. In addition, the temperature changes under an alternating magnetic field were observed. As in vitro tests, the magnetic responsiveness of chitosan- and starch-coated magnetite was determined by a simple blood vessel model under various intensities of magnetic field. L929 normal cells and KB carcinoma cells were used to examine the cytotoxicity and affinity of each sample using the MTT method. The chitosan-coated magnetic nanoparticles generated a higher DeltaT of 23 degrees C under an AC magnetic field than the starch-coated magnetite, and the capturing rate of the particles was 96% under an external magnetic field of 0.4 T. The highest viability of L929 cells was 93.7%. Comparing the rate of KB cells capture with the rate of L929 cells capture, the rate of KB cells capture relatively increased with 10.8% in chitosan-coated magnetic nanoparticles. Hence, chitosan-coated magnetic nanoparticles are biocompatible and have a selective affinity to KB cells. The targeting of magnetic nanoparticles in hyperthermia was improved using a controlled magnetic field and a chitosan-coating. Therefore, chitosan-coated magnetic nanoparticles are expected to be promising materials for use in magnetic targeted hyperthermia. 2008 Wiley Periodicals, Inc.
The use of superconductivity in magnetic balance design
NASA Technical Reports Server (NTRS)
Moss, F. E.
1973-01-01
The magnetic field and field gradient requirements for magnetic suspension in a Mach 3, 6-in. diameter wind tunnel are stated, along with the power requirements for gradient coil pairs wound of copper operating at room temperature and aluminum cooled to 20 K. The power dissipated is large enough that the use of superconductivity in the coil design becomes an attractive alternative. The problems of stability and ac losses are outlined along with the properties of stabilized superconductors. A brief review of a simplified version of the critical state model of C. P. Bean is presented, and the problems involved in calculations of the ac losses in superconducting coils are outlined. A summary of ac loss data taken on pancake coils wound of commercially available Nb3Sn partially stabilized tape is presented and shown as leading to the U.Va. gradient coil design. The actual coil performance is compared with predictions based on the BNL results. Finally, some remarks are presented concerning scaling of the ac losses to larger magnetic suspension systems as well as prospects for improved performance using newer multifilament superconductors.
Bearingless AC Homopolar Machine Design and Control for Distributed Flywheel Energy Storage
NASA Astrophysics Data System (ADS)
Severson, Eric Loren
The increasing ownership of electric vehicles, in-home solar and wind generation, and wider penetration of renewable energies onto the power grid has created a need for grid-based energy storage to provide energy-neutral services. These services include frequency regulation, which requires short response-times, high power ramping capabilities, and several charge cycles over the course of one day; and diurnal load-/generation-following services to offset the inherent mismatch between renewable generation and the power grid's load profile, which requires low self-discharge so that a reasonable efficiency is obtained over a 24 hour storage interval. To realize the maximum benefits of energy storage, the technology should be modular and have minimum geographic constraints, so that it is easily scalable according to local demands. Furthermore, the technology must be economically viable to participate in the energy markets. There is currently no storage technology that is able to simultaneously meet all of these needs. This dissertation focuses on developing a new energy storage device based on flywheel technology to meet these needs. It is shown that the bearingless ac homopolar machine can be used to overcome key obstacles in flywheel technology, namely: unacceptable self-discharge and overall system cost and complexity. Bearingless machines combine the functionality of a magnetic bearing and a motor/generator into a single electromechanical device. Design of these machines is particularly challenging due to cross-coupling effects and trade-offs between motor and magnetic bearing capabilities. The bearingless ac homopolar machine adds to these design challenges due to its 3D flux paths requiring computationally expensive 3D finite element analysis. At the time this dissertation was started, bearingless ac homopolar machines were a highly immature technology. This dissertation advances the state-of-the-art of these machines through research contributions in the areas of
Input current shaped ac-to-dc converters
NASA Technical Reports Server (NTRS)
1985-01-01
Input current shaping techniques for ac-to-dc converters were investigated. Input frequencies much higher than normal, up to 20 kHz were emphasized. Several methods of shaping the input current waveform in ac-to-dc converters were reviewed. The simplest method is the LC filter following the rectifier. The next simplest method is the resistor emulation approach in which the inductor size is determined by the converter switching frequency and not by the line input frequency. Other methods require complicated switch drive algorithms to construct the input current waveshape. For a high-frequency line input, on the order of 20 kHz, the simple LC cannot be discarded so peremptorily, since the inductor size can be compared with that for the resistor emulation method. In fact, since a dc regulator will normally be required after the filter anyway, the total component count is almost the same as for the resistor emulation method, in which the filter is effectively incorporated into the regulator.
Magnetism in curved geometries
NASA Astrophysics Data System (ADS)
Streubel, Robert
Deterministically bending and twisting two-dimensional structures in the three-dimensional (3D) space provide means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape. The recent developments of 3D curved magnetic geometries, ranging from theoretical predictions over fabrication to characterization using integral means as well as advanced magnetic tomography, will be reviewed. Theoretical works predict a curvature-induced effective anisotropy and effective Dzyaloshinskii-Moriya interaction resulting in a vast of novel effects including magnetochiral effects (chirality symmetry breaking) and topologically induced magnetization patterning. The remarkable development of nanotechnology, e.g. preparation of high-quality extended thin films, nanowires and frameworks via chemical and physical deposition as well as 3D nano printing, has granted first insights into the fundamental properties of 3D shaped magnetic objects. Optimizing magnetic and structural properties of these novel 3D architectures demands new investigation methods, particularly those based on vector tomographic imaging. Magnetic neutron tomography and electron-based 3D imaging, such as electron holography and vector field electron tomography, are well-established techniques to investigate macroscopic and nanoscopic samples, respectively. At the mesoscale, the curved objects can be investigated using the novel method of magnetic X-ray tomography. In spite of experimental challenges to address the appealing theoretical predictions of curvature-induced effects, those 3D magnetic architectures have already proven their application potential for life sciences, targeted delivery, realization of 3D spin-wave filters, and magneto-encephalography devices, to name just a few. DOE BES MSED (DE-AC02-05-CH11231).
Gallasch, Eugen; Rafolt, Dietmar; Postruznik, Magdalena; Fresnoza, Shane; Christova, Monica
2018-04-19
Rotation of a static magnet over the motor cortex (MC) generates a transcranial alternating magnetic field (tAMF), and a linked alternating electrical field. The aim of this transcranial magnetic stimulation (TMS) study is to investigate whether such fields are able to influence MC excitability, and whether there are parallels to tACS induced effects. Fourteen healthy volunteers received 20 Hz tAMF stimulation over the MC, over the vertex, and 20 Hz tACS over the MC, each with a duration of 15 min. TMS assessments were performed before and after the interventions. Changes in motor evoked potentials (MEP), short interval intra-cortical inhibition (SICI) and intra-cortical facilitation (ICF) were evaluated. The tACS and the tAMF stimulation over the MC affected cortical excitability in a different way. After tAMF stimulation MEP amplitudes and ICF decreased and the effect of SICI increased. After tACS MEP amplitudes increased and there were no effects on SICI and ICF. The recorded single and paired pulse MEPs indicate a general decrease of MC excitability following 15 min of tAMF stimulation. The effects demonstrate that devices based on rotating magnets are potentially suited to become a novel brain stimulation tool in clinical neurophysiology. Copyright © 2018 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.
Levels in 227Ac populated in the 230Th( p, α) reaction
NASA Astrophysics Data System (ADS)
Burke, D. G.; Garrett, P. E.; Qu, Tao
2003-09-01
The 230,232Th(p, α) 227,229Ac reactions were studied using 20 MeV protons and a magnetic spectrograph to analyze the reaction products. Relative populations of levels in 229Ac correlated well with previously published (t, α) results for the same final levels, showing that the similarity of the two reactions observed empirically in the deformed rare earth region extends to actinides. The most strongly populated level in 227Ac is at 639 keV, and is assigned as the 1/2 +[4 0 0] bandhead. The 435 keV level, previously adopted as the 1/2 +[6 6 0] bandhead, also has a significant intensity that is attributed to Δ N=2 mixing between these two K=1/2 proton orbitals. The Δ N=2 matrix element estimated from these data is ˜80 keV, similar to values observed for the same two Nilsson states as neutron orbitals in the dysprosium isotopes.
Mishra, Om P.; Popov, Anatoliy V.; Pietrofesa, Ralph A.; Christofidou-Solomidou, Melpo
2017-01-01
Background Secoisolariciresinol diglucoside (SDG), the main lignan in whole grain flaxseed, is a potent antioxidant and free radical scavenger with known radioprotective properties. However, the exact mechanism of SDG radioprotection is not well understood. The current study identified a novel mechanism of DNA radioprotection by SDG in physiological solutions by scavenging active chlorine species (ACS) and reducing chlorinated nucleobases. Methods The ACS scavenging activity of SDG was determined using two highly specific fluoroprobes: hypochlorite-specific 3′-(p-aminophenyl) fluorescein (APF) and hydroxyl radical-sensitive 3′-(p-hydroxyphenyl) fluorescein (HPF). Dopamine, an SDG structural analog, was used for proton 1H NMR studies to trap primary ACS radicals. Taurine N-chlorination was determined to demonstrate radiation-induced generation of hypochlorite, a secondary ACS. DNA protection was assessed by determining the extent of DNA fragmentation and plasmid DNA relaxation following exposure to ClO− and radiation. Purine base chlorination by ClO− and γ-radiation was determined by using 2-aminopurine (2-AP), a fluorescent analog of 6-aminopurine. Results: Chloride anions (Cl−) consumed >90% of hydroxyl radicals in physiological solutions produced by γ-radiation resulting in ACS formation, which was detected by 1H NMR. Importantly, SDG scavenged hypochlorite- and γ-radiation-induced ACS. In addition, SDG blunted ACS-induced fragmentation of calf thymus DNA and plasmid DNA relaxation. SDG treatment before or after ACS exposure decreased the ClO− or γ-radiation-induced chlorination of 2-AP. Exposure to γ-radiation resulted in increased taurine chlorination, indicative of ClO− generation. NMR studies revealed formation of primary ACS radicals (chlorine atoms (Cl•) and dichloro radical anions (Cl2−•)), which were trapped by SDG and its structural analog dopamine. Conclusion We demonstrate that γ-radiation induces the generation of ACS in
The historical development of the magnetic method in exploration
Nabighian, M.N.; Grauch, V.J.S.; Hansen, R.O.; LaFehr, T.R.; Li, Y.; Peirce, J.W.; Phillips, J.D.; Ruder, M.E.
2005-01-01
The magnetic method, perhaps the oldest of geophysical exploration techniques, blossomed after the advent of airborne surveys in World War II. With improvements in instrumentation, navigation, and platform compensation, it is now possible to map the entire crustal section at a variety of scales, from strongly magnetic basement at regional scale to weakly magnetic sedimentary contacts at local scale. Methods of data filtering, display, and interpretation have also advanced, especially with the availability of low-cost, high-performance personal computers and color raster graphics. The magnetic method is the primary exploration tool in the search for minerals. In other arenas, the magnetic method has evolved from its sole use for mapping basement structure to include a wide range of new applications, such as locating intrasedimentary faults, defining subtle lithologic contacts, mapping salt domes in weakly magnetic sediments, and better defining targets through 3D inversion. These new applications have increased the method's utility in all realms of exploration - in the search for minerals, oil and gas, geothermal resources, and groundwater, and for a variety of other purposes such as natural hazards assessment, mapping impact structures, and engineering and environmental studies. ?? 2005 Society of Exploration Geophysicists. All rights reserved.
NASA Astrophysics Data System (ADS)
Dutta, Papia; Mandal, S. K.; Dey, P.; Nath, A.
2018-04-01
We have presented the ac electrical properties and dielectric studies of 0.5 NiFe2O4 - 0.5 ZnO multiferroic nanocomposites prepared through low temperature "pyrophoric reaction process". Structural characterization has been carried out through X-ray diffraction technique, which shows the co-existence of both the phases of the nanocomposites. The ac electrical properties of nanocomposites have been studied employing impedance spectroscopy technique. The impedance value is found to increase with increase in magnetic field attributing the magnetostriction property of the composites. Dielectric constant is found to decrease with both the increase in magnetic fields and temperatures. Studies of dielectric constant reveal the Maxwell Wagner interfacial polarization at low frequency regime. Relaxation frequency as a function of magnetic fields and temperatures is found to shift towards the high frequency region.
This patent describes a low offset AC correlator avoids DC offset and low frequency noise by frequency operating the correlation signal so that low...noise, low level AC amplification can be substituted for DC amplification. Subsequently, the high level AC signal is demodulated to a DC level. (Author)
NASA Astrophysics Data System (ADS)
Shmavonyan, Gagik; Zadoyan, Ovsanna
2013-03-01
Magnetic systems with reduced dimensionality make good test beds for checks on theoretical models. Here, changes in the nature of magnetic ordering in quasi-2d system of layered Ni hydroxides (LH-Ni-) with variations in the interlayer spacing c are investigated. Magnetic properties of LH-Ni-DS with c ~ 30 A° synthesized by intercalating dodecyl sulfate ion, (C12H25OSO3)- between the layers are compared with those of LH-Ni-Ac (c ~ 8.5 A°) containing the acetate (Ac) ligand. Measurements included those of magnetization M vs. T and H, ac susceptibilities (f = 0.1 Hz - 1000 Hz) and EMR (Electron Magnetic Resonance) spectra at 9.28 GHz. Results show that just like LH-Ni-Ac, LH-Ni-DS also orders ferromagnetically but with Tc ~ 23 Kabout 45 % largerthanT c 16 Kreportedfor LH-Ni-Ac.. In EMR studies, linewidth is strongly temperature-dependent, decreasing with decreasing T from 300 K, reaching a minimum near 45 K and then increasing sharply for T < 45 K, the latter due to short range magnetic ordering. These results differ with the model of Drillon et al in which interlayer dipolar interaction between clusters of correlated spins in the layers yields TC nearly independent of c. Roles of magnetic anisotropy and exchange constants in determining TC in the LH-Ni systems is discussed.
Tools and Setups for Experiments with AC and Rotating Magnetic Fields
ERIC Educational Resources Information Center
Ponikvar, D.
2010-01-01
A rotating magnetic field is the basis for the transformation of electrical energy to mechanical energy. School experiments on the rotating magnetic field are rare since they require the use of specially prepared mechanical setups and/or relatively large, three-phase power supplies to achieve strong magnetic fields. This paper proposes several…
An AC-electromagnetic bearing for flywheel energy storage in space
NASA Technical Reports Server (NTRS)
Nikolajsen, Jorgen L.
1993-01-01
A repulsive type AC-electromagnetic bearing was developed and tested. It was conceived on the basis of the so-called Magnetic River suspension for high-speed trains. The appearance of the bearing is similar to the traditional DC-type electromagnetic bearing but the operating principle is different. The magnets are fed with alternating current instead of direct current and the rotor is fitted with a conducting sleeve (e.g. aluminum) instead of a ferromagnetic sleeve. The repulsion is due to induction of eddy-currents in the conducting sleeve. The bearing is inherently stable and requires no feedback control. It provides support in five degrees of freedom such that a short rotor may be fully supported by a single bearing. These capabilities were demonstrated experimentally. On the down side, the load carrying capacity and the damping obtained so far were quite low compared to the DC-type bearing. Also, significant heating of the conducting sleeve was experienced. The AC-bearing is essentially a modified induction motor and there are strong indications that it can be run both as a motor and as a generator with no commutator requirements. It is therefore considered to be a good candidate for support of energy storage flywheels in space.
A rolling locomotion method for untethered magnetic microrobots
NASA Astrophysics Data System (ADS)
Hou, Max T.; Shen, Hui-Mei; Jiang, Guan-Lin; Lu, Chiang-Ni; Hsu, I.-Jen; Yeh, J. Andrew
2010-01-01
It is a challenge to achieve free and efficient motion of microrobots on arbitrary surfaces. We report a rolling locomotion method for a magnetic microrobot with a rectangular body (300×200×50 μm3); this method is based on an external rotating magnetic field. The magnetic force, accompanied by normal and friction forces, enables the successive rotations of the microrobot. A magnetic field with a rotational speed of 2 rps rolls the microrobot, giving it a translation speed of 1.4 mm/s. With this locomotion ability, microrobots can move along a line or curve and can climb slopes or stairs.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Eccles, Cynthia L.; Patel, Ritesh; Simeonov, Anna K.
2011-02-01
Purpose: Abdominal compression (AC) can be used to reduce respiratory liver motion in patients undergoing liver stereotactic body radiotherapy. The purpose of the present study was to measure the changes in three-dimensional liver tumor motion with and without compression using cine-magnetic resonance imaging. Patients and Methods: A total of 60 patients treated as a part of an institutional research ethics board-approved liver stereotactic body radiotherapy protocol underwent cine T2-weighted magnetic resonance imaging through the tumor centroid in the coronal and sagittal planes. A total of 240 cine-magnetic resonance imaging sequences acquired at one to three images each second for 30-60more » s were evaluated using an in-house-developed template matching tool (based on the coefficient correlation) to measure the magnitude of the tumor motion. The average tumor edge displacements were used to determine the magnitude of changes in the caudal-cranial (CC) and anteroposterior (AP) directions, with and without AC. Results: The mean tumor motion without AC of 11.7 mm (range, 4.8-23.3) in the CC direction was reduced to 9.4 mm (range, 1.6-23.4) with AC. The tumor motion was reduced in both directions (CC and AP) in 52% of the patients and in a single direction (CC or AP) in 90% of the patients. The mean decrease in tumor motion with AC was 2.3 and 0.6 mm in the CC and AP direction, respectively. Increased motion occurred in one or more directions in 28% of patients. Clinically significant (>3 mm) decreases were observed in 40% and increases in <2% of patients in the CC direction. Conclusion: AC can significantly reduce three-dimensional liver tumor motion in most patients, although the magnitude of the reduction was smaller than previously reported.« less
Apparatus and method for magnetically processing a specimen
Ludtka, Gerard M; Ludtka, Gail M; Wilgen, John B; Kisner, Roger A; Jaramillo, Roger A
2013-09-03
An apparatus for magnetically processing a specimen that couples high field strength magnetic fields with the magnetocaloric effect includes a high field strength magnet capable of generating a magnetic field of at least 1 Tesla and a magnetocaloric insert disposed within a bore of the high field strength magnet. A method for magnetically processing a specimen includes positioning a specimen adjacent to a magnetocaloric insert within a bore of a magnet and applying a high field strength magnetic field of at least 1 Tesla to the specimen and to the magnetocaloric insert. The temperature of the specimen changes during the application of the high field strength magnetic field due to the magnetocaloric effect.
Yan, Guang; Xu, Qingfang; Anissimov, Yuri G; Hao, Jinsong; Higuchi, William I; Li, S Kevin
2008-03-01
As a continuing effort to understand the mechanisms of alternating current (AC) transdermal iontophoresis and the iontophoretic transport pathways in the stratum corneum (SC), the objectives of the present study were to determine the interplay of AC frequency, AC voltage, and iontophoretic transport of ionic and neutral permeants across human epidermal membrane (HEM) and use AC as a means to characterize the transport pathways. Constant AC voltage iontophoresis experiments were conducted with HEM in 0.10 M tetraethyl ammonium pivalate (TEAP). AC frequencies ranging from 0.0001 to 25 Hz and AC applied voltages of 0.5 and 2.5 V were investigated. Tetraethyl ammonium (TEA) and arabinose (ARA) were the ionic and neutral model permeants, respectively. In data analysis, the logarithm of the permeability coefficients of HEM for the model permeants was plotted against the logarithm of the HEM electrical resistance for each AC condition. As expected, linear correlations between the logarithms of permeability coefficients and the logarithms of resistances of HEM were observed, and the permeability data were first normalized and then compared at the same HEM electrical resistance using these correlations. Transport enhancement of the ionic permeant was significantly larger than that of the neutral permeant during AC iontophoresis. The fluxes of the ionic permeant during AC iontophoresis of 2.5 V in the frequency range from 5 to 1,000 Hz were relatively constant and were approximately 4 times over those of passive transport. When the AC frequency decreased from 5 to 0.001 Hz at 2.5 V, flux enhancement increased to around 50 times over passive transport. While the AC frequency for achieving the full effect of iontophoretic enhancement at low AC frequency was lower than anticipated, the frequency for approaching passive diffusion transport at high frequency was higher than expected from the HEM morphology. These observations are consistent with a transport model of multiple
A polyvalent harmonic coil testing method for small-aperture magnets
NASA Astrophysics Data System (ADS)
Arpaia, Pasquale; Buzio, Marco; Golluccio, Giancarlo; Walckiers, Louis
2012-08-01
A method to characterize permanent and fast-pulsed iron-dominated magnets with small apertures is presented. The harmonic coil measurement technique is enhanced specifically for small-aperture magnets by (1) in situ calibration, for facing search-coil production inaccuracy, (2) rotating the magnet around its axis, for correcting systematic effects, and (3) measuring magnetic fluxes by stationary coils at different angular positions for measuring fast pulsed magnets. This method allows a quadrupole magnet for particle accelerators to be characterized completely, by assessing multipole field components, magnetic axis position, and field direction. In this paper, initially the metrological problems arising from testing small-aperture magnets are highlighted. Then, the basic ideas of the proposed method and the architecture of the corresponding measurement system are illustrated. Finally, experimental validation results are shown for small-aperture permanent and fast-ramped quadrupole magnets for the new linear accelerator Linac4 at CERN (European Organization for Nuclear Research).
Method for reducing snap in magnetic amplifiers
NASA Technical Reports Server (NTRS)
Fischer, R. L. E.; Word, J. L.
1968-01-01
Method of reducing snap in magnetic amplifiers uses a degenerative feedback circuit consisting of a resistor and a separate winding on a magnetic core. The feedback circuit extends amplifier range by allowing it to be used at lower values of output current.
A component compensation method for magnetic interferential field
NASA Astrophysics Data System (ADS)
Zhang, Qi; Wan, Chengbiao; Pan, Mengchun; Liu, Zhongyan; Sun, Xiaoyong
2017-04-01
A new component searching with scalar restriction method (CSSRM) is proposed for magnetometer to compensate magnetic interferential field caused by ferromagnetic material of platform and improve measurement performance. In CSSRM, the objection function for parameter estimation is to minimize magnetic field (components and magnitude) difference between its measurement value and reference value. Two scalar compensation method is compared with CSSRM and the simulation results indicate that CSSRM can estimate all interferential parameters and external magnetic field vector with high accuracy. The magnetic field magnitude and components, compensated with CSSRM, coincide with true value very well. Experiment is carried out for a tri-axial fluxgate magnetometer, mounted in a measurement system with inertial sensors together. After compensation, error standard deviation of both magnetic field components and magnitude are reduced from more than thousands nT to less than 20 nT. It suggests that CSSRM provides an effective way to improve performance of magnetic interferential field compensation.
New methods of magnet-based instrumentation for NOTES.
Magdeburg, Richard; Hauth, Daniel; Kaehler, Georg
2013-12-01
Laparoscopic surgery has displaced open surgery as the standard of care for many clinical conditions. NOTES has been described as the next surgical frontier with the objective of incision-free abdominal surgery. The principal challenge of NOTES procedures is the loss of triangulation and instrument rigidity, which is one of the fundamental concepts of laparoscopic surgery. To overcome these problems necessitates the development of new instrumentation. material and methods: We aimed to assess the use of a very simple combination of internal and external magnets that might allow the vigorous multiaxial traction/counter-traction required in NOTES procedures. The magnet retraction system consisted of an external magnetic assembly and either small internal magnets attached by endoscopic clips to the designated tissue (magnet-clip-approach) or an endoscopic grasping forceps in a magnetic deflector roll (magnet-trocar-approach). We compared both methods regarding precision, time and efficacy by performing transgastric partial uterus resections with better results for the magnet-trocar-approach. This proof-of-principle animal study showed that the combination of external and internal magnets generates sufficient coupling forces at clinically relevant abdominal wall thicknesses, making them suitable for use and evaluation in NOTES procedures, and provides the vigorous multiaxial traction/counter-traction required by the lack of additional abdominal trocars.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Jenrow, K.A.; Smith, C.H.; Liboff, A.R.
1996-12-31
The authors recently reported that cephalic regeneration in the planarian Dugesia tigrina was significantly delayed in populations exposed continuously to combined parallel DC and AC magnetic fields. This effect was consistent with hypotheses suggesting an underlying resonance phenomenon. The authors report here, in a parallel series of investigations on the same model system, that the incidence of regeneration anomalies presenting as tumor-like protuberances also increases significantly (P < .001) in association with exposure to weak 60 Hz magnetic fields, with peak intensities ranging between 1.0 and 80.0 {micro}T. These anomalies often culminate in the complete disaggregation of the organism. Similarmore » to regeneration rate effects, the incidence of regeneration anomalies is specifically dependent upon the planaria possessing a fixed orientation with respect to the applied magnetic field vectors. However, unlike the regeneration rate effects, the AC magnetic field alone, in the absence of any measurable DC field, is capable of producing these anomalies. Moreover, the incidence of regeneration anomalies follows a clear dose-response relationship as a function of AC magnetic field intensity, with the threshold for induced electric field intensity estimated at 5 {micro} V/m. The addition of either 51.1 or 78.4 {micro}T DC magnetic fields, applied in parallel combination with the AC field, enhances the appearance of anomalies relative to the 60 Hz AC field alone, but only at certain AC field intensities. Thus, whereas the previous study of regeneration rate effects appeared to involve exclusively resonance interactions, the regeneration anomalies reported here appear to result primarily from Faraday induction coupling.« less
Development of magneto-rheologial fluid (MRF) based clutch for output torque control of AC motors
NASA Astrophysics Data System (ADS)
Nguyen, Q. Hung; Do, H. M. Hieu; Nguyen, V. Quoc; Nguyen, N. Diep; Le, D. Thang
2018-03-01
In industry, the AC motor is widely used because of low price, power availability, low cost maintenance. The main disadvantages of AC motors compared to DC motors are difficulty in speed and torque control, requiring expensive controllers with complex control algorithms. This is the basic limitations in the widespread adoption of AC motor systems for industrial automation. One feasible solution for AC motor control is using MRF (magneto-rheological fluid) based clutches (shortly called MR clutches) Although there have been many studies on MR clutches, most of these clutches used traditional configuration with coils wound on the middle cylindrical part and a compotator is used to supply power to the coils. Therefore, this type of MR clutches possesses many disadvantages such as high friction and unstable applied current due to commutator, complex structure which causes difficulty in manufacture, assembly, and maintenance. In addition, the bottleneck problem of magnetic field is also a challenging issue. In this research, we will develop a new type of MR clutches that overcomes the abovementioned disadvantages of traditional MR clutches and more suitable for application in controlling of AC motor. Besides, in this study, speed and torque control system for AC motors using developed MR clutches is designed and experimental validated.
Ac electroosmotic flows above coplanar electrodes
NASA Astrophysics Data System (ADS)
Kweon Suh, Yong
2009-03-01
Interactive numerical method has been proposed to calculate the ac electroosmotic flows above a pair of coplanar electrodes. The thin electrical triple layer (ETL) has been modeled by an asymptotic theory developed by the authors. The model corresponds to a simple dynamic equation for the surface charge density representing the integrated charge over the inner layer. Interactive calculation of the dynamic equation and the Laplace equation for several periods of ac frequency then yielded steady-state distribution of potential and the potential drop across the Stern and inner layers. The Smoluchowski's slip velocity was then determined from those two set of data and used as the boundary condition for the calculation of the Stokes' flow above the electrodes. We have shown that our solutions compared well with the experimental data reported in the literature. We investigated the effect of various parameters on the slip velocity distribution, such as the ac frequency, the electrode length, the effective Stern-layer thickness and the adsorption coefficients.
Distinguishing magnetic blocking and surface spin-glass freezing in nickel ferrite nanoparticles
NASA Astrophysics Data System (ADS)
Nadeem, K.; Krenn, H.; Traussing, T.; Letofsky-Papst, I.
2011-01-01
Nickel ferrite nanoparticles dispersed in SiO2 matrix have been synthesized by sol-gel method. Structural analysis has been performed by using x-ray diffraction and transmission electron microscopy. Magnetic properties have been investigated by using superconducting quantum interference device magnetometry. In addition to the average blocking temperature peak at TB=120 K measured by a zero field cooled temperature scan of the dc susceptibility, an additional hump near 15 K is observed. Temperature dependent out-of-phase ac susceptibility shows the same features: one broad peak at high temperature and a second narrow peak at low temperature. The high temperature peak corresponds to magnetic blocking of individual nanoparticles, while the low temperature peak is attributed to surface spin-glass freezing which becomes dominant for decreasing particle diameter. To prove the dynamics of the spin (dis)order in both regimes of freezing and blocking, the frequency dependent ac susceptibility is investigated under a biasing dc field. The frequency shift in the "frozen" low-temperature ac susceptibility peak is fitted to a dynamic scaling law with a critical exponent zv=7.5, which indicates a spin-glass phase. Exchange bias is turned on at low temperature which signifies the existence of a strong core-shell interaction. Aging and memory effects are further unique fingerprints of a spin-glass freezing on the surface of isolated magnetic nanoparticles.
Linear ac Response of Thin Superconductors during Flux Creep
NASA Astrophysics Data System (ADS)
Brandt, Ernst Helmut; Gurevich, Alexander
1996-03-01
The linear magnetic susceptibility χ\\(ω\\) of superconducting strips and disks in a transverse magnetic field is calculated in the flux-creep regime. It is shown that χ\\(ω\\) = χ'-iχ'' for ω>>1/t is universal, independent of temperature, dc field, and material parameters, depending only on the sample shape, ac frequency ω/2π, and time t elapsed after creep has started. Qualitatively, χ\\(ω\\) can be obtained from the χ\\(ω\\) of metallic conductors by replacing the Ohmic relaxation time by t. At ωt>>1, which may apply down to rather low frequencies, the dissipative flux-creep state exhibits a nearly Meissner-like response with χ' = -1+0.40/ωt and χ'' = 0.25ln\\(29ωt\\)/ωt for disks.
NASA Technical Reports Server (NTRS)
Hein, R. A.; Hojaji, H.; Barkatt, A.; Shafii, H.; Michael, K. A.; Thorpe, A. N.; Ware, M. F.; Alterescu, S.
1989-01-01
A comparison of the low magnetic field properties of sintered (990 C) and partially melted samples (1050 C) has been performed. Changes in the microstructure produced by recrystallization from the melt result in a significant increase in flux pinning at 77 K. Low-frequency (10-100 Hz), low-ac magnetic-field (0.01-9.0 Oe) ac susceptibility data show that gross changes in the loss component accompany the observed changes in microstructure. The effects of applied dc magnetic fields (10-220 Oe) on the ac responses of these microstructures have also been probed.
Segmented media and medium damping in microwave assisted magnetic recording
NASA Astrophysics Data System (ADS)
Bai, Xiaoyu; Zhu, Jian-Gang
2018-05-01
In this paper, we present a methodology of segmented media stack design for microwave assisted magnetic recording. Through micro-magnetic modeling, it is demonstrated that an optimized media segmentation is able to yield high signal-to-noise ratio even with limited ac field power. With proper segmentation, the ac field power could be utilized more efficiently and this can alleviate the requirement for medium damping which has been previously considered a critical limitation. The micro-magnetic modeling also shows that with segmentation optimization, recording signal-to-noise ratio can have very little dependence on damping for different recording linear densities.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Guo, Y.; Pariat, E.; Moraitis, K.
We study the writhe, twist, and magnetic helicity of different magnetic flux ropes, based on models of the solar coronal magnetic field structure. These include an analytical force-free Titov–Démoulin equilibrium solution, non-force-free magnetohydrodynamic simulations, and nonlinear force-free magnetic field models. The geometrical boundary of the magnetic flux rope is determined by the quasi-separatrix layer and the bottom surface, and the axis curve of the flux rope is determined by its overall orientation. The twist is computed by the Berger–Prior formula, which is suitable for arbitrary geometry and both force-free and non-force-free models. The magnetic helicity is estimated by the twistmore » multiplied by the square of the axial magnetic flux. We compare the obtained values with those derived by a finite volume helicity estimation method. We find that the magnetic helicity obtained with the twist method agrees with the helicity carried by the purely current-carrying part of the field within uncertainties for most test cases. It is also found that the current-carrying part of the model field is relatively significant at the very location of the magnetic flux rope. This qualitatively explains the agreement between the magnetic helicity computed by the twist method and the helicity contributed purely by the current-carrying magnetic field.« less
Numerical simulation of bubble deformation in magnetic fluids by finite volume method
NASA Astrophysics Data System (ADS)
Yamasaki, Haruhiko; Yamaguchi, Hiroshi
2017-06-01
Bubble deformation in magnetic fluids under magnetic field is investigated numerically by an interface capturing method. The numerical method consists of a coupled level-set and VOF (Volume of Fluid) method, combined with conservation CIP (Constrained Interpolation Profile) method with the self-correcting procedure. In the present study considering actual physical properties of magnetic fluid, bubble deformation under given uniform magnetic field is analyzed for internal magnetic field passing through a magnetic gaseous and liquid phase interface. The numerical results explain the mechanism of bubble deformation under presence of given magnetic field.
Several fluidic tuned AC Amplifiers were designed and tested. Interstage tuning and feedback designs are considered. Good results were obtained...corresponding Q’s as high as 12. Element designs and test results of one, two, and three stage amplifiers are presented. AC Modulated Carrier Systems
Wang, Zhengjun; Seehra, Mohindar S
2016-04-06
Previous magnetic studies in the organic semiconductor β-manganese phthalocyanine (β-MnPc) have reported it to be a canted ferromagnet below T(C) ≈ 8.6 K. However, the recent result of the lack of a λ-type anomaly in the specific heat versus temperature data near the quoted T(C) has questioned the presence of long-range 3-dimensional (3D) magnetic ordering in this system. In this paper, detailed measurements and analysis of the temperature (2 K-300 K) and magnetic field (up to 90 kOe) dependence of the dc and ac magnetic susceptibilities in a powder sample of β-MnPc leads us to conclude that 3D long-range magnetic ordering is absent in this material. This is supported by the Arrott plots and the lack of a peak in the ac susceptibilities, χ' and χ″, near the quoted T(C). Instead, the system can be best described as an Ising-like chain magnet with Arrhenius relaxation of the magnetization governed by an intra-layer ferromagnetic exchange constant J/k(B) = 2.6 K and the single ion anisotropy energy parameter |D|/k(B) = 8.3 K. The absence of 3D long range order is consistent with the measured |D|/ > J.
Magnetic Field Analysis of Lorentz Motors Using a Novel Segmented Magnetic Equivalent Circuit Method
Qian, Junbing; Chen, Xuedong; Chen, Han; Zeng, Lizhan; Li, Xiaoqing
2013-01-01
A simple and accurate method based on the magnetic equivalent circuit (MEC) model is proposed in this paper to predict magnetic flux density (MFD) distribution of the air-gap in a Lorentz motor (LM). In conventional MEC methods, the permanent magnet (PM) is treated as one common source and all branches of MEC are coupled together to become a MEC network. In our proposed method, every PM flux source is divided into three sub-sections (the outer, the middle and the inner). Thus, the MEC of LM is divided correspondingly into three independent sub-loops. As the size of the middle sub-MEC is small enough, it can be treated as an ideal MEC and solved accurately. Combining with decoupled analysis of outer and inner MECs, MFD distribution in the air-gap can be approximated by a quadratic curve, and the complex calculation of reluctances in MECs can be avoided. The segmented magnetic equivalent circuit (SMEC) method is used to analyze a LM, and its effectiveness is demonstrated by comparison with FEA, conventional MEC and experimental results. PMID:23358368
Biosensing utilizing magnetic markers and superconducting quantum interference devices
NASA Astrophysics Data System (ADS)
Enpuku, Keiji; Tsujita, Yuya; Nakamura, Kota; Sasayama, Teruyoshi; Yoshida, Takashi
2017-05-01
Magnetic biosensing techniques that are based on the use of bio-functionalized magnetic nanoparticles (magnetic markers) and superconducting quantum interference devices (SQUIDs) are expected to have various advantages when compared with conventional biosensing methods. In this paper, we review the recent progress made in magnetic biosensing techniques. First, we describe the most important parameters of magnetic markers that are intended for use in biosensing, i.e., the magnetic signal and the relaxation time that are determined by the Brownian and/or Néel relaxation mechanisms. We note that these parameters are significantly dependent on the marker size, and as a result, commercial markers exhibit a wide variety of values for these key parameters. Next, we describe three measurement methods that have been developed based on the magnetic properties of these markers, i.e., AC susceptibility, relaxation and remanence-based measurement methods. The weak (picotesla-range) signals emitted by the markers can be measured precisely with a SQUID system using these methods. Finally, we give examples of biosensing for in vitro and in vivo medical diagnosis applications. For in vitro diagnosis, high-sensitivity detection of various biological targets has been demonstrated without use of any washing process to separate the bound and free markers. For in vivo applications, detection of the quantities and the three-dimensional positions of the markers that have been injected into the test subject are demonstrated. These results confirm the effectiveness of magnetic biosensing techniques.
Optimal Power Scheduling for a Medium Voltage AC/DC Hybrid Distribution Network
Zhu, Zhenshan; Liu, Dichen; Liao, Qingfen; ...
2018-01-26
With the great increase of renewable generation as well as the DC loads in the distribution network; DC distribution technology is receiving more attention; since the DC distribution network can improve operating efficiency and power quality by reducing the energy conversion stages. This paper presents a new architecture for the medium voltage AC/DC hybrid distribution network; where the AC and DC subgrids are looped by normally closed AC soft open point (ACSOP) and DC soft open point (DCSOP); respectively. The proposed AC/DC hybrid distribution systems contain renewable generation (i.e., wind power and photovoltaic (PV) generation); energy storage systems (ESSs); softmore » open points (SOPs); and both AC and DC flexible demands. An energy management strategy for the hybrid system is presented based on the dynamic optimal power flow (DOPF) method. The main objective of the proposed power scheduling strategy is to minimize the operating cost and reduce the curtailment of renewable generation while meeting operational and technical constraints. The proposed approach is verified in five scenarios. The five scenarios are classified as pure AC system; hybrid AC/DC system; hybrid system with interlinking converter; hybrid system with DC flexible demand; and hybrid system with SOPs. Results show that the proposed scheduling method can successfully dispatch the controllable elements; and that the presented architecture for the AC/DC hybrid distribution system is beneficial for reducing operating cost and renewable generation curtailment.« less
Optimal Power Scheduling for a Medium Voltage AC/DC Hybrid Distribution Network
DOE Office of Scientific and Technical Information (OSTI.GOV)
Zhu, Zhenshan; Liu, Dichen; Liao, Qingfen
With the great increase of renewable generation as well as the DC loads in the distribution network; DC distribution technology is receiving more attention; since the DC distribution network can improve operating efficiency and power quality by reducing the energy conversion stages. This paper presents a new architecture for the medium voltage AC/DC hybrid distribution network; where the AC and DC subgrids are looped by normally closed AC soft open point (ACSOP) and DC soft open point (DCSOP); respectively. The proposed AC/DC hybrid distribution systems contain renewable generation (i.e., wind power and photovoltaic (PV) generation); energy storage systems (ESSs); softmore » open points (SOPs); and both AC and DC flexible demands. An energy management strategy for the hybrid system is presented based on the dynamic optimal power flow (DOPF) method. The main objective of the proposed power scheduling strategy is to minimize the operating cost and reduce the curtailment of renewable generation while meeting operational and technical constraints. The proposed approach is verified in five scenarios. The five scenarios are classified as pure AC system; hybrid AC/DC system; hybrid system with interlinking converter; hybrid system with DC flexible demand; and hybrid system with SOPs. Results show that the proposed scheduling method can successfully dispatch the controllable elements; and that the presented architecture for the AC/DC hybrid distribution system is beneficial for reducing operating cost and renewable generation curtailment.« less
Modelling ac ripple currents in HTS coated conductors
NASA Astrophysics Data System (ADS)
Xu, Zhihan; Grilli, Francesco
2015-10-01
Dc transmission using high temperature superconducting (HTS) coated conductors (CCs) offers a promising solution to the globally growing demand for effective, reliable and economic transmission of green energy up to the gigawatt level over very long distances. The credible estimation of the losses and thereby the heat dissipation involved, where ac ripples (introduced in rectification/ac-dc conversion) are viewed as a potential source of notable contribution, is highly essential for the rational design of practical HTS dc transmission cables and corresponding cryogenic systems to fulfil this demand. Here we report a targeted modelling study into the ac losses in a HTS CC subject to dc and ac ripple currents simultaneously, by solving Maxwell’s equations using the finite element method (FEM) in the commercial software package COMSOL. It is observed that the instantaneous loss exhibits only one peak per cycle in the HTS CC subject to sinusoidal ripples, given that the amplitude of the ac ripples is smaller than approximately 20% of that of the dc current. This is a distinct contrast to the usual observation of two peaks per cycle in a HTS CC subject to ac currents only. The unique mechanism is also revealed, which is directly associated with the finding that, around any local minima of the applied ac ripples, the critical state of -J c is never reached at the edges of the HTS CC, as it should be according to the Bean model. When running further into the longer term, it is discovered that the ac ripple loss of the HTS CC in full-wave rectification decays monotonically, at a speed which is found to be insensitive to the frequency of the applied ripples within our targeted situations, to a relatively low level of approximately 1.38 × 10-4 W m-1 in around 1.7 s. Comparison between this level and other typical loss contributions in a HTS dc cable implies that ac ripple currents in HTS CCs should only be considered as a minor source of dissipation in superconducting dc
NASA Astrophysics Data System (ADS)
Yu, Jun; Hao, Du; Li, Decai
2018-01-01
The phenomenon whereby an object whose density is greater than magnetic fluid can be suspended stably in magnetic fluid under the magnetic field is one of the peculiar properties of magnetic fluids. Examples of applications based on the peculiar properties of magnetic fluid are sensors and actuators, dampers, positioning systems and so on. Therefore, the calculation and measurement of magnetic levitation force of magnetic fluid is of vital importance. This paper concerns the peculiar second-order buoyancy experienced by a magnet immersed in magnetic fluid. The expression for calculating the second-order buoyancy was derived, and a novel method for calculating and measuring the second-order buoyancy was proposed based on the expression. The second-order buoyancy was calculated by ANSYS and measured experimentally using the novel method. To verify the novel method, the second-order buoyancy was measured experimentally with a nonmagnetic rod stuck on the top surface of the magnet. The results of calculations and experiments show that the novel method for calculating the second-order buoyancy is correct with high accuracy. In addition, the main causes of error were studied in this paper, including magnetic shielding of magnetic fluid and the movement of magnetic fluid in a nonuniform magnetic field.
Performance trends of rehabilitated AC pavements
DOT National Transportation Integrated Search
2000-10-01
The General Pavement Study (GPS) 6 experiment, "AC Overlay of AC Pavements," involves pavement test sections where an asphalt concrete (AC) overlay was placed on an existing AC pavement. This TechBrief summarizes the results of a study of the GPS-6 e...
Method and apparatus for control of a magnetic structure
Challenger, Michael P.; Valla, Arthur S.
1996-06-18
A method and apparatus for independently adjusting the spacing between opposing magnet arrays in charged particle based light sources. Adjustment mechanisms between each of the magnet arrays and the supporting structure allow the gap between the two magnet arrays to be independently adjusted. In addition, spherical bearings in the linkages to the magnet arrays permit the transverse angular orientation of the magnet arrays to also be adjusted. The opposing magnet arrays can be supported above the ground by the structural support.
NASA Astrophysics Data System (ADS)
D'Andrea, M.; Argan, A.; Lotti, S.; Macculi, C.; Piro, L.; Biasotti, M.; Corsini, D.; Gatti, F.; Torrioli, G.
2016-07-01
The ATHENA observatory is the second large-class mission in ESA Cosmic Vision 2015-2025, with a launch foreseen in 2028 towards the L2 orbit. The mission addresses the science theme "The Hot and Energetic Universe", by coupling a high-performance X-ray Telescope with two complementary focal-plane instruments. One of these is the X-ray Integral Field Unit (X-IFU): it is a TES based kilo-pixel order array able to provide spatially resolved high-resolution spectroscopy (2.5 eV at 6 keV) over a 5 arcmin FoV. The X-IFU sensitivity is degraded by the particles background expected at L2 orbit, which is induced by primary protons of both galactic and solar origin, and mostly by secondary electrons. To reduce the background level and enable the mission science goals, a Cryogenic Anticoincidence (CryoAC) detector is placed < 1 mm below the TES array. It is a 4- pixel TES based detector, with wide Silicon absorbers sensed by Ir:Au TESes. The CryoAC development schedule foresees by Q1 2017 the delivery of a Demonstration Model (DM) to the X-IFU FPA development team. The DM is a single-pixel detector that will address the final design of the CryoAC. It will verify some representative requirements at single-pixel level, especially the detector operation at 50 mK thermal bath and the threshold energy at 20 keV. To reach the final DM design we have developed and tested the AC-S7 prototype, with 1 cm2 absorber area sensed by 65 Ir TESes. Here we will discuss the pulse analysis of this detector, which has been illuminated by the 60 keV line from a 241Am source. First, we will present the analysis performed to investigate pulses timings and spectrum, and to disentangle the athermal component of the pulses from the thermal one. Furthermore, we will show the application to our dataset of an alternative method of pulse processing, based upon Principal Component Analysis (PCA). This kind of analysis allow us to recover better energy spectra than achievable with traditional methods
Rock-Magnetic Method for Post Nuclear Detonation Diagnostics
NASA Astrophysics Data System (ADS)
Englert, J.; Petrosky, J.; Bailey, W.; Watts, D. R.; Tauxe, L.; Heger, A. S.
2011-12-01
A magnetic signature characteristic of a Nuclear Electromagnetic Pulse (NEMP) may still be detectable near the sites of atmospheric nuclear tests conducted at what is now the Nevada National Security Site. This signature is due to a secondary magnetization component of the natural remanent magnetization of material containing traces of ferromagnetic particles that have been exposed to a strong pulse of magnetic field. We apply a rock-magnetic method introduced by Verrier et al. (2002), and tested on samples exposed to artificial lightning, to samples of rock and building materials (e.g. bricks, concrete) retrieved from several above ground nuclear test sites. The results of magnetization measurements are compared to NEMP simulations and historic test measurements.
NASA Astrophysics Data System (ADS)
Guiffard, B.; Seveno, R.
2015-01-01
In this study, we report the magnetically induced electric field E 3 in Pb(Zr0.57Ti0.43)O3 (PZT) thin films, when they are subjected to both dynamic magnetic induction (magnitude B ac at 45 kHz) and static magnetic induction ( B dc) generated by a coil and a single permanent magnet, respectively. It is found that highest sensitivity to B dc——is achieved for the thin film with largest effective electrode. This magnetoelectric (ME) effect is interpreted in terms of coupling between eddy current-induced Lorentz forces (stress) in the electrodes of PZT and piezoelectricity. Such coupling was evidenced by convenient modelling of experimental variations of electric field magnitude with both B ac and B dc induction magnitudes, providing imperfect open circuit condition was considered. Phase angle of E 3 versus B dc could also be modelled. At last, the results show that similar to multilayered piezoelectric-magnetostrictive composite film, a PZT thin film made with a simple manufacturing process can behave as a static or dynamic magnetic field sensor. In this latter case, a large ME voltage coefficient of under B dc = 0.3 T was found. All these results may provide promising low-cost magnetic energy harvesting applications with microsized systems.
NASA Technical Reports Server (NTRS)
Roth, Don J.
1991-01-01
The purpose of this dissertation was the following: (1) to characterize the effect of pore fraction on a comprehensive set of electrical and magnetic properties for the yttrium-barium-copper-oxide (YBCO) high temperature ceramic superconductor; and (2) to determine the viability of using a room-temperature, nondestructive characterization method to aid in the prediction of superconducting (cryogenic) properties. The latter involved correlating ultrasonic velocity measurements at room temperature with property-affecting pore fraction and oxygen content variations. The use of ultrasonic velocity for estimating pore fraction in YBCO is presented, and other polycrystalline materials are reviewed, modeled, and statistically analyzed. This provides the basis for using ultrasonic velocity to interrogate microstructure. The effect of pore fraction (0.10-0.25) on superconductor properties of YBCO samples was characterized. Spatial (within-sample) variations in microstructure and superconductor properties were investigated, and the effect of oxygen content on elastic behavior was examined. Experimental methods used included a.c. susceptibility, electrical, and ultrasonic velocity measurements. Superconductor properties measured included transition temperature, magnetic transition width, transport and magnetic critical current density, magnetic shielding, a.c. loss, and sharpness of the voltage-current characteristics. An ultrasonic velocity image constructed from measurements at 1mm increments across a YBCO sample revealed microstructural variations that correlated with variations in magnetic shielding and a.c. loss behavior. Destructive examination using quantitative image analysis revealed pore fraction to be the varying microstructural feature.
Thermally Assisted Macroscopic Quantum Resonance on a Single-Crystal of Mn12-ac
NASA Astrophysics Data System (ADS)
Lionti, F.; Thomas, L.; Ballou, R.; Wernsdorfer, W.; Barbara, B.; Sulpice, A.; Sessoli, R.; Gatteschi, D.
1997-03-01
Magnetization measurements have been performed on a single mono-crystal of the molecule Mn12-acetate (L. Thomas, F. Lionti, R. Ballou, R. Sessoli, D. Gatteschi and B. Barbara, Nature, 383, 145 (1996).). Steps were observed in the hysteresis loop for values of the applied field at which level crossings of the collective spin states of each manganese clusters take place. The influence of quartic terms is taken into account. At these fields, the magnetization relaxes at short time scales, being otherwise essentially blocked. This novel behavior is interpreted in terms of resonant quantum tunneling of the magnetization from thermally activated energy levels. Hysteresis loop measurements performed for different field orientations and ac-susceptibility experiments, confirm general trends of this picture.
Dual phase magnetic material component and method of forming
Dial, Laura Cerully; DiDomizio, Richard; Johnson, Francis
2017-04-25
A magnetic component having intermixed first and second regions, and a method of preparing that magnetic component are disclosed. The first region includes a magnetic phase and the second region includes a non-magnetic phase. The method includes mechanically masking pre-selected sections of a surface portion of the component by using a nitrogen stop-off material and heat-treating the component in a nitrogen-rich atmosphere at a temperature greater than about 900.degree. C. Both the first and second regions are substantially free of carbon, or contain only limited amounts of carbon; and the second region includes greater than about 0.1 weight % of nitrogen.
Luczak, Susan E; Rosen, I Gary
2014-08-01
Transdermal alcohol sensor (TAS) devices have the potential to allow researchers and clinicians to unobtrusively collect naturalistic drinking data for weeks at a time, but the transdermal alcohol concentration (TAC) data these devices produce do not consistently correspond with breath alcohol concentration (BrAC) data. We present and test the BrAC Estimator software, a program designed to produce individualized estimates of BrAC from TAC data by fitting mathematical models to a specific person wearing a specific TAS device. Two TAS devices were worn simultaneously by 1 participant for 18 days. The trial began with a laboratory alcohol session to calibrate the model and was followed by a field trial with 10 drinking episodes. Model parameter estimates and fit indices were compared across drinking episodes to examine the calibration phase of the software. Software-generated estimates of peak BrAC, time of peak BrAC, and area under the BrAC curve were compared with breath analyzer data to examine the estimation phase of the software. In this single-subject design with breath analyzer peak BrAC scores ranging from 0.013 to 0.057, the software created consistent models for the 2 TAS devices, despite differences in raw TAC data, and was able to compensate for the attenuation of peak BrAC and latency of the time of peak BrAC that are typically observed in TAC data. This software program represents an important initial step for making it possible for non mathematician researchers and clinicians to obtain estimates of BrAC from TAC data in naturalistic drinking environments. Future research with more participants and greater variation in alcohol consumption levels and patterns, as well as examination of gain scheduling calibration procedures and nonlinear models of diffusion, will help to determine how precise these software models can become. Copyright © 2014 by the Research Society on Alcoholism.
Advanced quantitative magnetic nondestructive evaluation methods - Theory and experiment
NASA Technical Reports Server (NTRS)
Barton, J. R.; Kusenberger, F. N.; Beissner, R. E.; Matzkanin, G. A.
1979-01-01
The paper reviews the scale of fatigue crack phenomena in relation to the size detection capabilities of nondestructive evaluation methods. An assessment of several features of fatigue in relation to the inspection of ball and roller bearings suggested the use of magnetic methods; magnetic domain phenomena including the interaction of domains and inclusions, and the influence of stress and magnetic field on domains are discussed. Experimental results indicate that simplified calculations can be used to predict many features of these results; the data predicted by analytic models which use finite element computer analysis predictions do not agree with respect to certain features. Experimental analyses obtained on rod-type fatigue specimens which show experimental magnetic measurements in relation to the crack opening displacement and volume and crack depth should provide methods for improved crack characterization in relation to fracture mechanics and life prediction.
1991-05-01
ib qeocie. Thki document may not be rdeaed for open publicado. untit hu been deared by die appropriate military seavice or a veunent agency. AC /RC...A N/A N/A 11. TITLE (Include Security Classification) AC /RC Force Structure Integraticn 12. PERSONAL AUTHOR(S) Russell A. Eggers 13a. TYPE OF REPORT... AC ) and Reserve Components (RC) Force Integration is critical in today’s Total Army. The Army of soldiers, Active and Reserve, exists to play a key
Magnetic Amplifier-Based Power-Flow Controller
Dimitrovski, Aleksandar; Li, Zhi; Ozpineci, Burak
2015-02-05
The concept of the magnetic amplifier, a common electromagnetic device in electronic applications in the past, has seldom been used in power systems. In this paper, we introduce the magnetic amplifier-based power-flow controller (MAPFC), an innovative low-cost device that adopts the idea of the magnetic amplifier for power-flow control applications. The uniqueness of MAPFC is in the use of the magnetization of the ferromagnetic core, shared by an ac and a dc winding, as the medium to control the ac winding reactance inserted in series with the transmission line to be controlled. Large power flow in the line can bemore » regulated by the small dc input to the dc winding. Moreover, a project on the R&D of an MAPFC has been funded by the U.S. Department of Energy (DOE) and conducted by the Oak Ridge National Laboratory (ORNL), the University of Tennessee-Knoxville, and Waukesha Electric Systems, Inc. since early 2012. Findings from the project are presented along with some results obtained in a laboratory environment.« less
Malik, V.; Goodwill, J.; Mallapragada, S.; ...
2014-11-13
The rate of heating of a water-based colloid of uniformly sized 15 nm magnetic nanoparticles by high-amplitude and high-frequency ac magnetic field induced by the resonating LC circuit (nanoTherics Magnetherm) was measured. The results are analyzed in terms of specific energy absorption rate (SAR). Fitting field amplitude and frequency dependences of SAR to the linear response theory, magnetic moment per particles was extracted. The value of magnetic moment was independently evaluated from dc magnetization measurements (Quantum Design MPMS) of a frozen colloid by fitting field-dependent magnetization to Langevin function. The two methods produced similar results, which are compared to themore » theoretical expectation for this particle size. Additionally, analysis of SAR curves yielded effective relaxation time.« less
Phase-transitional Fe3O4/perfluorohexane Microspheres for Magnetic Droplet Vaporization.
Wang, Ronghui; Zhou, Yang; Zhang, Ping; Chen, Yu; Gao, Wei; Xu, Jinshun; Chen, Hangrong; Cai, Xiaojun; Zhang, Kun; Li, Pan; Wang, Zhigang; Hu, Bing; Ying, Tao; Zheng, Yuanyi
2017-01-01
Activating droplets vaporization has become an attractive strategy for ultrasound imaging and physical therapy due to the significant increase in ultrasound backscatter signals and its ability to physically damage the tumor cells. However, the current two types of transitional droplets named after their activation methods have their respective limitations. To circumvent the limitations of these activation methods, here we report the concept of magnetic droplet vaporization (MDV) for stimuli-responsive cancer theranostics by a magnetic-responsive phase-transitional agent. This magnetic-sensitive phase-transitional agent-perfluorohexane (PFH)-loaded porous magnetic microspheres (PFH-PMMs), with high magnetic-thermal energy-transfer capability, could quickly respond to external alternating current (AC) magnetic fields to produce thermal energy and trigger the vaporization of the liquid PFH. We systematically demonstrated MDV both in vitro and in vivo. This novel trigger method with deep penetration can penetrate the air-filled viscera and trigger the vaporization of the phase-transitional agent without the need of pre-focusing lesion. This unique MDV strategy is expected to substantially broaden the biomedical applications of nanotechnology and promote the clinical treatment of tumors that are not responsive to chemical therapies.
NASA Technical Reports Server (NTRS)
Ohi, Nobuaki; Makinen, Carla P.; Mitchell, Richard; Moisan, Tiffany A.
2008-01-01
Ocean color algorithms are based on the parameterization of apparent optical properties as a function of inherent optical properties. WET Labs underwater absorption and attenuation meters (ac-9 and ac-s) measure both the spectral beam attenuation [c (lambda)] and absorption coefficient [a (lambda)]. The ac-s reports in a continuous range of 390-750 nm with a band pass of 4 nm, totaling approximately 83 distinct wavelengths, while the ac-9 reports at 9 wavelengths. We performed the ac-s field measurements at nine stations in the Mid-Atlantic Bight from water calibrations to data analysis. Onboard the ship, the ac-s was calibrated daily using Milli Q-water. Corrections for the in situ temperature and salinity effects on optical properties of water were applied. Corrections for incomplete recovery of the scattered light in the ac-s absorption tube were performed. The fine scale of spectral and vertical distributions of c (lambda) and a (lambda) were described from the ac-s. The significant relationships between a (674) and that of spectrophotometric analysis and chlorophyll a concentration of discrete water samples were observed.
NASA Astrophysics Data System (ADS)
Mahmoud, Mohamed E.; Khalifa, Mohamed A.; El Wakeel, Yasser M.; Header, Mennatllah S.; Abdel-Fattah, Tarek M.
2017-04-01
A novel magnetic nanosorbent was designed using chemical grafting of nano-magnetite (Nano-Fe3O4) with nanolayer of activated carbon (AC) via urea intermediate for the formation of Nano-Fe3O4-Urea-AC. Characterizing was carried out using FT-IR, SEM, HR-TEM, TGA, point of zero charge (Pzc) and surface area analysis. The designed sorbent maintained its magnetic properties and nanosized structure in the range of 8.7-14.1 nm. The surface area was identified as 389 m2/g based on the BET method. Sorption of uranyl ions from aqueous solutions was studied and evaluated in different experimental conditions. Removal of uranyl ions increased with increasing in pH value and the maximum percentage removal was established at pH 5.0. The removal and sorption processes of uranyl ions by Nano-Fe3O4-Urea-AC sorbent were studied and optimized using the batch technique. The key variables affecting removal of uranyl ions were studied including the effect of the contact time, dosage of Nano-Fe3O4-Urea-AC sorbent, reaction temperature, initial uranyl ions concentration and interfering anions and cations.
Frequency dependence of magnetic ac loss in a Roebel cable made of YBCO on a Ni-W substrate
NASA Astrophysics Data System (ADS)
Lakshmi, L. S.; Staines, M. P.; Badcock, R. A.; Long, N. J.; Majoros, M.; Collings, E. W.; Sumption, M. D.
2010-08-01
We have investigated the frequency dependent contributions to the magnetic ac loss in a 10 strand Roebel cable with 2 mm wide non-insulated strands and a transposition length of 90 mm. This cable is made from 40 mm wide YBCO coated conductor tape manufactured by AMSC and stabilized by electroplating 25 µm thick copper on either side prior to the mechanical punching of the cable strands. The measurements were carried out in both perpendicular and parallel field orientation, at frequencies in the range of 30-200 Hz. While the loss in the perpendicular orientation is predominantly hysteretic in nature, we observe some frequency dependence of the loss when the cable approaches full flux penetration at high field amplitudes. The magnitude is consistent with eddy current losses in the copper stabilization layer. This supports the fact that the inter-strand coupling loss is not significant in this frequency range. In the parallel field orientation, the hysteresis loss in the Ni-W alloy substrate dominates, but we see an unusually strong frequency dependent contribution to the loss which we attribute to intra-strand current loops.
Shlapa, Yulia; Solopan, Sergii; Bodnaruk, Andrii; Kulyk, Mykola; Kalita, Viktor; Tykhonenko-Polishchuk, Yulia; Tovstolytkin, Alexandr; Belous, Anatolii
2017-12-01
Two sets of Nd-doped La 0.7 Sr 0.3 MnO 3 nanoparticles were synthesized via sol-gel method with further heat treatment at 1073 and 1573 K, respectively. Crystallographic and magnetic properties of obtained nanoparticles were studied, and the effect of synthesis conditions on these properties was investigated. According to X-ray data, all particles crystallized in the distorted perovskite structure. Magnetic parameters, such as saturation magnetization, coercivity, Curie temperature, and specific loss power, which is released on the exposure of an ensemble of nanoparticles to AC magnetic field, were determined for both sets of samples. The correlation between the values of Curie temperature and maximal heating temperature under AC magnetic field was found. It was revealed that for the samples synthesized at 1573 K, the dependences of crystallographic and magnetic parameters on Nd content were monotonous, while for the samples synthesized at 1073 K, they were non-monotonous. It was concluded that Nd-doped La 0.7 Sr 0.3 MnO 3 nanoparticles are promising materials for self-controlled magnetic hyperthermia applications, but the researchers should be aware of the unusual behavior of the particles synthesized at relatively low temperatures.
Method for obtaining large levitation pressure in superconducting magnetic bearings
Hull, John R.
1997-01-01
A method and apparatus for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap.
Method for obtaining large levitation pressure in superconducting magnetic bearings
Hull, John R.
1996-01-01
A method and apparatus for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap.
NASA Astrophysics Data System (ADS)
Kondo, Keiichiro; Hata, Hiroshi; Yuki, Kazuaki; Naganuma, Katsunori; Matsuoka, Koichi; Hasebe, Toshio
This paper is aimed at providing the designing method of a permanent magnet synchronous motor (PMSM) control system for the high-speed and the single-phase AC powered Gauge Changing Train (GCT). The state-of-the-art electrical motive unit is equipped with downsized direct drive type PMSMs for the simplified gauge changeable truck. Due to the feeding the AC single phase power, we propose a beat-less control for PMSMs. We verify the development results of designing procedures by the experimental results of operation on a high-speed test line in Colorado, USA.
Method and apparatus for assembling permanent magnet rotors
Hsu, J.S.; Adams, D.J.
1999-06-22
A permanent magnet assembly for assembly in large permanent magnet motors and generators includes a two-piece carrier that can be slid into a slot in the rotor and then secured in place using a set screw. The invention also provides an auxiliary carrier device with guide rails that line up with the teeth of the rotor, so that a permanent magnet assembly can be pushed first into a slot, and then down the slot to its proper location. An auxiliary tool is provided to move the permanent magnet assembly into position in the slot before it is secured in place. Methods of assembling and disassembling the magnet assemblies in the rotor are also disclosed. 2 figs.
Method to manufacture bit patterned magnetic recording media
Raeymaekers, Bart; Sinha, Dipen N
2014-05-13
A method to increase the storage density on magnetic recording media by physically separating the individual bits from each other with a non-magnetic medium (so-called bit patterned media). This allows the bits to be closely packed together without creating magnetic "cross-talk" between adjacent bits. In one embodiment, ferromagnetic particles are submerged in a resin solution, contained in a reservoir. The bottom of the reservoir is made of piezoelectric material.
2013-01-01
Background Molecular imaging using magnetic nanoparticles (MNPs)—magnetic particle imaging (MPI)—has attracted interest for the early diagnosis of cancer and cardiovascular disease. However, because a steep local magnetic field distribution is required to obtain a defined image, sophisticated hardware is required. Therefore, it is desirable to realize excellent image quality even with low-performance hardware. In this study, the spatial resolution of MPI was evaluated using an image reconstruction method based on the correlation information of the magnetization signal in a time domain and by applying MNP samples made from biocompatible ferucarbotran that have adjusted particle diameters. Methods The magnetization characteristics and particle diameters of four types of MNP samples made from ferucarbotran were evaluated. A numerical analysis based on our proposed method that calculates the image intensity from correlation information between the magnetization signal generated from MNPs and the system function was attempted, and the obtained image quality was compared with that using the prototype in terms of image resolution and image artifacts. Results MNP samples obtained by adjusting ferucarbotran showed superior properties to conventional ferucarbotran samples, and numerical analysis showed that the same image quality could be obtained using a gradient magnetic field generator with 0.6 times the performance. However, because image blurring was included theoretically by the proposed method, an algorithm will be required to improve performance. Conclusions MNP samples obtained by adjusting ferucarbotran showed magnetizing properties superior to conventional ferucarbotran samples, and by using such samples, comparable image quality (spatial resolution) could be obtained with a lower gradient magnetic field intensity. PMID:23734917
Method and apparatus for measuring nuclear magnetic properties
Weitekamp, D.P.; Bielecki, A.; Zax, D.B.; Zilm, K.W.; Pines, A.
1987-12-01
A method for studying the chemical and structural characteristics of materials is disclosed. The method includes placement of a sample material in a high strength polarizing magnetic field to order the sample nuclei. The condition used to order the sample is then removed abruptly and the ordering of the sample allowed to evolve for a time interval. At the end of the time interval, the ordering of the sample is measured by conventional nuclear magnetic resonance techniques. 5 figs.
Method and apparatus for measuring nuclear magnetic properties
Weitekamp, Daniel P.; Bielecki, Anthony; Zax, David B.; Zilm, Kurt W.; Pines, Alexander
1987-01-01
A method for studying the chemical and structural characteristics of materials is disclosed. The method includes placement of a sample material in a high strength polarizing magnetic field to order the sample nucleii. The condition used to order the sample is then removed abruptly and the ordering of the sample allowed to evolve for a time interval. At the end of the time interval, the ordering of the sample is measured by conventional nuclear magnetic resonance techniques.
DOT National Transportation Integrated Search
2010-03-01
This document provides guidance for using the ACS Statistical Analyzer. It is an Excel-based template for users of estimates from the American Community Survey (ACS) to assess the precision of individual estimates and to compare pairs of estimates fo...
Method for obtaining large levitation pressure in superconducting magnetic bearings
Hull, J.R.
1997-08-05
A method and apparatus are disclosed for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap. 4 figs.
Method for obtaining large levitation pressure in superconducting magnetic bearings
Hull, J.R.
1996-10-08
A method and apparatus are disclosed for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap. 4 figs.
Apparatus and method for handling magnetic particles in a fluid
Holman, David A.; Grate, Jay W.; Bruckner-Lea, Cynthia J.
2000-01-01
The present invention is an apparatus and method for handling magnetic particles suspended in a fluid, relying upon the known features of a magnetic flux conductor that is permeable thereby permitting the magnetic particles and fluid to flow therethrough; and a controllable magnetic field for the handling. The present invention is an improvement wherein the magnetic flux conductor is a monolithic porous foam.
Improvement of immunoassay detection system by using alternating current magnetic susceptibility
NASA Astrophysics Data System (ADS)
Kawabata, R.; Mizoguchi, T.; Kandori, A.
2016-03-01
A major goal with this research was to develop a low-cost and highly sensitive immunoassay detection system by using alternating current (AC) magnetic susceptibility. We fabricated an improved prototype of our previously developed immunoassay detection system and evaluated its performance. The prototype continuously moved sample containers by using a magnetically shielded brushless motor, which passes between two anisotropic magneto resistance (AMR) sensors. These sensors detected the magnetic signal in the direction where each sample container passed them. We used the differential signal obtained from each AMR sensor's output to improve the signal-to-noise ratio (SNR) of the magnetic signal measurement. Biotin-conjugated polymer beads with avidin-coated magnetic particles were prepared to examine the calibration curve, which represents the relation between AC magnetic susceptibility change and polymer-bead concentration. For the calibration curve measurement, we, respectively, measured the magnetic signal caused by the magnetic particles by using each AMR sensor installed near the upper or lower part in the lateral position of the passing sample containers. As a result, the SNR of the prototype was 4.5 times better than that of our previous system. Moreover, the data obtained from each AMR sensor installed near the upper part in the lateral position of the passing sample containers exhibited an accurate calibration curve that represented good correlation between AC magnetic susceptibility change and polymer-bead concentration. The conclusion drawn from these findings is that our improved immunoassay detection system will enable a low-cost and highly sensitive immunoassay.
Improvement of immunoassay detection system by using alternating current magnetic susceptibility.
Kawabata, R; Mizoguchi, T; Kandori, A
2016-03-01
A major goal with this research was to develop a low-cost and highly sensitive immunoassay detection system by using alternating current (AC) magnetic susceptibility. We fabricated an improved prototype of our previously developed immunoassay detection system and evaluated its performance. The prototype continuously moved sample containers by using a magnetically shielded brushless motor, which passes between two anisotropic magneto resistance (AMR) sensors. These sensors detected the magnetic signal in the direction where each sample container passed them. We used the differential signal obtained from each AMR sensor's output to improve the signal-to-noise ratio (SNR) of the magnetic signal measurement. Biotin-conjugated polymer beads with avidin-coated magnetic particles were prepared to examine the calibration curve, which represents the relation between AC magnetic susceptibility change and polymer-bead concentration. For the calibration curve measurement, we, respectively, measured the magnetic signal caused by the magnetic particles by using each AMR sensor installed near the upper or lower part in the lateral position of the passing sample containers. As a result, the SNR of the prototype was 4.5 times better than that of our previous system. Moreover, the data obtained from each AMR sensor installed near the upper part in the lateral position of the passing sample containers exhibited an accurate calibration curve that represented good correlation between AC magnetic susceptibility change and polymer-bead concentration. The conclusion drawn from these findings is that our improved immunoassay detection system will enable a low-cost and highly sensitive immunoassay.
Magnetic manipulation of nanorods in the nucleus of living cells.
Celedon, Alfredo; Hale, Christopher M; Wirtz, Denis
2011-10-19
The organization of chromatin in the cell nucleus is crucial for gene expression regulation. However, physically probing the nuclear interior is challenging because high forces have to be applied using minimally invasive techniques. Here, magnetic nanorods embedded in the nucleus of living cells are subjected to controlled rotational forces, producing micron-sized displacements in the nuclear interior. The resulting time-dependent rotation of the nanorods is analyzed in terms of viscoelastic parameters of the nucleus, in wild-type and Lamin A/C deficient cells. This method and analysis reveal that Lamin A/C knockout, together perhaps with other changes that result from the knockout, induce significant decreases in the nuclear viscosity and elasticity. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.
Magnetic Diagnostics on the Magnetized Shock Experiment (MSX)
NASA Astrophysics Data System (ADS)
Hutchinson, T. M.; Weber, T. E.; Boguski, J. C.; Intrator, T. P.; Smith, R. J.; Dunn, J. P.
2013-10-01
The Magnetized Shock Experiment (MSX) at Los Alamos National Laboratory was built to investigate the physics of high-Alfvénic, supercritical, magnetized shocks through the acceleration and subsequent stagnation of a Field Reversed Configuration (FRC) plasmoid against a magnetic mirror and/or plasma target. An array of high-bandwidth, multi-axis, robust, internal magnetic probes has been constructed to characterize flux compression ratios, instability formation, and turbulent macro-scale features of the post-shock plasma. The mirror magnet is mounted on a linear translation stage, providing a capability to axially move the shock layer through the probe field of view. An independent, external probe array also provides conventional information on the FRC shape, velocity, and total pressure during the formation and acceleration phases. Probe design, characterization, configuration, and initial results are presented. This work is supported by the DOE OFES and NNSA under LANS contract DE-AC52-06NA25369. LA-UR-13-25189.
Dielectrophoretic particle-particle interaction under AC electrohydrodynamic flow conditions.
Lee, Doh-Hyoung; Yu, Chengjie; Papazoglou, Elisabeth; Farouk, Bakhtier; Noh, Hongseok M
2011-09-01
We used the Maxwell stress tensor method to understand dielectrophoretic particle-particle interactions and applied the results to the interpretation of particle behaviors under alternating current (AC) electrohydrodynamic conditions such as AC electroosmosis (ACEO) and electrothermal flow (ETF). Distinct particle behaviors were observed under ACEO and ETF. Diverse particle-particle interactions observed in experiments such as particle clustering, particles keeping a certain distance from each other, chain and disc formation and their rotation, are explained based on the numerical simulation data. The improved understanding of particle behaviors in AC electrohydrodynamic flows presented here will enable researchers to design better particle manipulation strategies for lab-on-a-chip applications. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
NASA Astrophysics Data System (ADS)
Cano, M. E.; Barrera, A.; Estrada, J. C.; Hernandez, A.; Cordova, T.
2011-11-01
The development of a device for generating ac magnetic fields based on a resonant inverter is presented, which has been specially designed to carry out experiments of magnetic hyperthermia. By determining the electric current in the LC resonant circuit, a maximum intensity of magnetic field around of 15 mT is calculated, with a frequency around of 206 kHz. This ac magnetic field is able to heat powdered magnetic materials embedded in biological systems to be used in biomedical applications. Indeed, in order to evaluate the sensitivity of the device we also present the measurements of the specific absorption rate in phantoms performed with commercially prepared Fe3O4 and distilled water at different concentrations.
Enhanced method of magnetic powder alignment for production of PLP Nd-Fe-B magnets
NASA Astrophysics Data System (ADS)
Popov, A. G.; Golovnia, O. A.; Protasov, A. V.
2017-04-01
It is demonstrated how the high degree of powder alignment in PLP magnets can be achieved by loading the powder into a container placed in a magnetic field of moderate strength. The strip-cast alloy with a composition of 30.00 Nd, 1.95 Dy, 66.42 Fe, 0.99 B, 0.54 Co, 0.1 Ga (wt%) was subjected to hydrogen decrepitation and then milled in a vibratory mill in toluene to an average particle size of 2.9 μm determined by the FSSS method. The powder was compacted in the magnetic field of 0.2 - 1.2 T to the filling density 2.6 - 3.2×103 kg/m3. It is shown that loading the powder into a container placed in a magnetic field enhances the degree of powder alignment in sintered Nd-Fe-B magnets produced from non-pressed powder. At the filling density less than 3.2×103 kg/m3, the density of magnets is high but insufficient, because of the formation of magnetostatic chains of particles, which impedes the powder compaction. The simulation by the discrete-element method qualitatively proves that the magnetostatic interaction of the chains of particles that are formed in the course of loading in the magnetic field stimulates a decrease in the density of the sintered magnets and its non-uniform distribution over the sample. As a result of the optimization of the parameters of the alignment and compaction of the powder loaded in a magnetic field, PLP magnets with Br ≥1.34 T, Hc ≥950 kA/m, (BH)max ≥340 kJ/m3, and the degree of alignment exceeding 96% were produced.
NMR system and method having a permanent magnet providing a rotating magnetic field
Schlueter, Ross D [Berkeley, CA; Budinger, Thomas F [Berkeley, CA
2009-05-19
Disclosed herein are systems and methods for generating a rotating magnetic field. The rotating magnetic field can be used to obtain rotating-field NMR spectra, such as magic angle spinning spectra, without having to physically rotate the sample. This result allows magic angle spinning NMR to be conducted on biological samples such as live animals, including humans.
Zaleski, Curtis M; Tricard, Simon; Depperman, Ezra C; Wernsdorfer, Wolfgang; Mallah, Talal; Kirk, Martin L; Pecoraro, Vincent L
2011-11-21
The magnetic behavior of the pentanuclear complex of formula Mn(II)(O(2)CCH(3))(2)[12-MC(Mn(III)(N)shi)-4](DMF)(6), 1, was investigated using magnetization and magnetic susceptibility measurements both in the solid state and in solution. Complex 1 has a nearly planar structure, made of a central Mn(II) ion surrounded by four peripheral Mn(III) ions. Solid state variable-field dc magnetic susceptibility experiments demonstrate that 1 possesses a low value for the total spin in the ground state; fitting appropriate expressions to the data results in antiferromangetic coupling both between the peripheral Mn(III) ions (J = -6.3 cm(-1)) and between the central Mn(II) ion and the Mn(III) ones (J' = -4.2 cm(-1)). In order to obtain a reasonable fit, a relatively large single ion magnetic anisotropy (D) value of 1 cm(-1) was necessary for the central Mn(II) ion. The single crystal magnetization measurements using a microsquid array display a very slight opening of the hysteresis loop but only at a very low temperature (0.04 K), which is in line with the ac susceptibility data where a slow relaxation of the magnetization occurs just around 2 K. In frozen solution, complex 1 displays a frequency dependent ac magnetic susceptibility signal with an energy barrier to magnetization reorientation (E) and relaxation time at an infinite temperature (τ(o)) of 14.7 cm(-1) and 1.4 × 10(-7) s, respectively, demonstrating the single molecule magnetic behavior in solution.
The AC photovoltaic module is here!
NASA Astrophysics Data System (ADS)
Strong, Steven J.; Wohlgemuth, John H.; Wills, Robert H.
1997-02-01
This paper describes the design, development, and performance results of a large-area photovoltaic module whose electrical output is ac power suitable for direct connection to the utility grid. The large-area ac PV module features a dedicated, integrally mounted, high-efficiency dc-to-ac power inverter with a nominal output of 250 watts (STC) at 120 Vac, 60 H, that is fully compatible with utility power. The module's output is connected directly to the building's conventional ac distribution system without need for any dc wiring, string combiners, dc ground-fault protection or additional power-conditioning equipment. With its advantages, the ac photovoltaic module promises to become a universal building block for use in all utility-interactive PV systems. This paper discusses AC Module design aspects and utility interface issues (including islanding).
Historic Methods for Capturing Magnetic Field Images
ERIC Educational Resources Information Center
Kwan, Alistair
2016-01-01
I investigated two late 19th-century methods for capturing magnetic field images from iron filings for historical insight into the pedagogy of hands-on physics education methods, and to flesh out teaching and learning practicalities tacit in the historical record. Both methods offer opportunities for close sensory engagement in data-collection…
A linear magnetic motor and generator
NASA Technical Reports Server (NTRS)
Studer, P. A.
1980-01-01
In linear magnetic motor and generator suitable for remote and hostile environments, magnetic forces drive reciprocating shaft along its axis. Actuator shaft is located in center of cylindrical body and may be supported by either contacting or noncontacting bearings. When device operates as bidirectional motor, drive coil selectively adds and subtracts magnetic flux to and from flux paths, producing forces that drive actuator along axis. When actuator is driven by external reciprocating engine, device becomes ac generator.
Magnetic sorbents added to soil slurries lower Cr aqueous concentration
NASA Astrophysics Data System (ADS)
Aravantinos, Konstantinos; Isari, Ekavi; Karapanagioti, Hrissi K.; Manariotis, Ioannis D.; Werner, David
2016-04-01
Activated carbon (AC) acts as a strong binding agent that lowers the pollutant concentration and, thus its toxicity. Another promising sorbent material in environmental applications is biochar (BC) which is obtained from the incomplete combustion of carbon-rich biomass under oxygen-limited conditions. Both of these materials could be used as soil or sediment amendments that would lower the toxicity in the aqueous phase. A draw back of this technique is that although the pollutant will remain non- bioavailable for many years being sorbed into these sorbents, it actually stays into the system. The objective of this study was (a) to synthesize a magnetic powdered activated carbon (AC/Fe) and magnetic powdered biochar (BC/Fe) produced from a commercial AC sample and BC, respectively and (b) to evaluate the potential use of AC/Fe and BC/Fe to lower Cr concentration that desorb from two soils in their soil slurries. The two soil samples originate from the vicinity of a local metal shop. The BC was produced from olive pomace. The surface area, the pore volume, and the average pore size of each sorbent were determined using gas (N2) adsorption-desorption cycles and the Brunauer, Emmett, and Teller (BET) equation. Isotherms with 30 adsorption and 20 desorption points were conducted at liquid nitrogen temperature (77K). Open surface area and micropore volume were determined using t-plot method and Harkins & Jura equation. For both AC/Fe, surface area measurements resulted in 66% those of corresponding AC. For BC/Fe, the surface area was 82% that of BC. Our previous studies have shown that both AC/Fe and BC/Fe are effective sorbents for mercury in aqueous solutions but with lower sorption capacity compared to the initial materials (50-75% lower). Batch experiments with all sorbent samples and each soil were conducted at room temperature (25oC) in order to compare the sorption properties of the materials. The soil slurries demonstrated low Cr concentrations (10.9 and 14.6
Methods for the fabrication of thermally stable magnetic tunnel junctions
Chang, Y Austin [Middleton, WI; Yang, Jianhua J [Madison, WI; Ladwig, Peter F [Hutchinson, MN
2009-08-25
Magnetic tunnel junctions and method for making the magnetic tunnel junctions are provided. The magnetic tunnel junctions are characterized by a tunnel barrier oxide layer sandwiched between two ferromagnetic layers. The methods used to fabricate the magnetic tunnel junctions are capable of completely and selectively oxidizing a tunnel junction precursor material using an oxidizing gas containing a mixture of gases to provide a tunnel junction oxide without oxidizing the adjacent ferromagnetic materials. In some embodiments the gas mixture is a mixture of CO and CO.sub.2 or a mixture of H.sub.2 and H.sub.2O.
Prasad, Thazhe Kootteri; Poneti, Giordano; Sorace, Lorenzo; Rodriguez-Douton, Maria Jesus; Barra, Anne-Laure; Neugebauer, Petr; Costantino, Luca; Sessoli, Roberta; Cornia, Andrea
2012-07-21
Tetrairon(III) complexes known as "ferric stars" have been functionalized with azobenzene groups to investigate the effect of light-induced trans-cis isomerization on single-molecule magnet (SMM) behaviour. According to DC magnetic data and EPR spectroscopy, clusters dispersed in polystyrene (4% w/w) exhibit the same spin (S = 5) and magnetic anisotropy as bulk samples. Ligand photoisomerization, achieved by irradiation at 365 nm, has no detectable influence on static magnetic properties. However, it induces a small but significant acceleration of magnetic relaxation as probed by AC susceptometry. The pristine behaviour can be almost quantitatively recovered by irradiation with white light. Our studies demonstrate that magnetic and optical bistability can be made to coexist in SMM materials, which are of current interest in molecular spintronics.
Study of dielectric relaxation and AC conductivity of InP:S single crystal
NASA Astrophysics Data System (ADS)
El-Nahass, M. M.; Ali, H. A. M.; El-Shazly, E. A.
2012-07-01
The dielectric relaxation and AC conductivity of InP:S single crystal were studied in the frequency range from 100 to 5.25 × 105 Hz and in the temperature range from 296 to 455 K. The dependence of the dielectric constant (ɛ1) and the dielectric loss (ɛ2) on both frequency and temperature was investigated. Since no peak was observed on the dielectric loss, we used a method based on the electric modulus to evaluate the activation energy of the dielectric relaxation. Scaling of the electric modulus spectra showed that the charge transport dynamics is independent of temperature. The AC conductivity (σAC) was found to obey the power law: Aωs. Analysis of the AC conductivity data and the frequency exponent showed that the correlated barrier hopping (CBH) model is the dominant mechanism for the AC conduction. The variation of AC conductivity with temperature at different frequencies showed that σAC is a thermally activated process.
Optical and magnetic properties of porous anodic alumina/Ni nanocomposite films
NASA Astrophysics Data System (ADS)
Zhang, Jing-Jing; Li, Zi-Yue; Zhang, Zhi-Jun; Wu, Tian-Shan; Sun, Hui-Yuan
2013-06-01
A simple method to tune the optical properties of porous anodic alumina (PAA) films embedded with Ni is reported. The films display highly saturated colors after being synthesized by an ac electrodeposition method. The optical properties of the samples can be effectively tuned by varying the oxidation time of aluminum. The ultrashort Ni nanowires (100 nm long and 50 nm in diameter) present only fcc phase and show no apparent averaged effective magnetic anisotropy. The coercivity mechanism of the Ni nanowires in our case is consistent with fanning mechanism based on a chain-of-spheres model. PAA/Ni films with structural color and magnetic properties have friability-resistant feature and can be used in many areas, including decoration, display, and multifunctional anti-counterfeiting technology.
Sub-micrometer particles produced by a low-powered AC electric arc in liquids.
Jaworski, Jacek A; Fleury, Eric
2012-01-01
The article presents the report of the production of composites of sub-micrometer metal particles in matrix consisted of the metal compounds by means of an AC electric arc in water and paraffin solutions using electrodes carbon-metal and metal-metal (metal: Ni, Fe, Co, Cu). The advantage of this method is the low electric power (from 5 to 10 W) needed in comparison to standard DC arc-discharge methods (0.8 to 3 kW). This method enables the production of particles from conductive material also in wide range of temperature and in solvent which could be either transparent to light or opaque. Moreover the solvent can be electrolyte or insulating liquid. The microstructure of the composite layer was investigated by scanning electron microscopy (SEM), Electron Probe Microanalysis (EPMA) and X-ray. During particles production in water metal oxides were created. Additionally using cobalt-copper, nickel-copper as couple electrodes, insoluble in water copper (II) hydroxide crystal grains were created additionally which crystals shape was depended on transition metal. For iron-copper couple electrodes system the copper (II) hydroxide was not formed. Experiments with sequence production of Ni and Fe particles with C electrode assisting in molten paraffin let to obtain both Ni and Fe particles surrounded by paraffin. After solidification the material was insulator but if locally magnetic field influenced on the liquid solution in that place after solidification a new composite was created which was electric current conductor with resistivity around 0.1 omega x m, was attracted by magnetic field and presented magneto resistance around 0.4% in changing magnetic field in a range 150 mT. After mixing the concentrated paraffin with normal paraffin resistivity of the mixture increased and it became photosensitive and created small voltage under light influence.
First AC loss test and analysis of a Bi2212 cable-in-conduit conductor for fusion application
NASA Astrophysics Data System (ADS)
Qin, Jinggang; Shi, Yi; Wu, Yu; Li, Jiangang; Wang, Qiuliang; He, Yuxiang; Dai, Chao; Liu, Fang; Liu, Huajun; Mao, Zhehua; Nijhuis, Arend; Zhou, Chao; Devred, Arnaud
2018-01-01
The main goal of the Chinese fusion engineering test reactor (CFETR) is to build a fusion engineering tokamak reactor with a fusion power of 50-200 MW, and plan to test the breeding tritium during the fusion reaction. This may require a maximum magnetic field of the central solenoid and toroidal field coils up to 15 T. New magnet technologies should be developed for the next generation of fusion reactors with higher requirements. Bi2Sr2CaCu2Ox (Bi2212) is considered as a potential and promising superconductor for the magnets in the CFETR. R&D activities are ongoing at the Institute of Plasma Physics, Chinese Academy of Sciences for demonstration of the feasibility of a CICC based on Bi2212 round wire. One sub-size conductor cabled with 42 wires was designed, manufactured and tested with limited strand indentation during cabling and good transport performance. In this paper, the first test results and analysis on the AC loss of Bi2212 round wires and cabled conductor samples are presented. Furthermore, the impact of mechanical load on the AC loss of the sub-size conductor is investigated to represent the operation conditions with electromagnetic loads. The first tests provide an essential basis for the validation of Bi2212 CICC and its application in fusion magnets.
Quantum control of topological defects in magnetic systems
NASA Astrophysics Data System (ADS)
Takei, So; Mohseni, Masoud
2018-02-01
Energy-efficient classical information processing and storage based on topological defects in magnetic systems have been studied over the past decade. In this work, we introduce a class of macroscopic quantum devices in which a quantum state is stored in a topological defect of a magnetic insulator. We propose noninvasive methods to coherently control and read out the quantum state using ac magnetic fields and magnetic force microscopy, respectively. This macroscopic quantum spintronic device realizes the magnetic analog of the three-level rf-SQUID qubit and is built fully out of electrical insulators with no mobile electrons, thus eliminating decoherence due to the coupling of the quantum variable to an electronic continuum and energy dissipation due to Joule heating. For a domain wall size of 10-100 nm and reasonable material parameters, we estimate qubit operating temperatures in the range of 0.1-1 K, a decoherence time of about 0.01-1 μ s , and the number of Rabi flops within the coherence time scale in the range of 102-104 .
High bandwidth magnetically isolated signal transmission circuit
NASA Technical Reports Server (NTRS)
Repp, John Donald (Inventor)
2005-01-01
Many current electronic systems incorporate expensive or sensitive electrical components. Because electrical energy is often generated or transmitted at high voltages, the power supplies to these electronic systems must be carefully designed. Power supply design must ensure that the electrical system being supplied with power is not exposed to excessive voltages or currents. In order to isolate power supplies from electrical equipment, many methods have been employed. These methods typically involve control systems or signal transfer methods. However, these methods are not always suitable because of their drawbacks. The present invention relates to transmitting information across an interface. More specifically, the present invention provides an apparatus for transmitting both AC and DC information across a high bandwidth magnetic interface with low distortion.
O'Donnell, Sharon; McKee, Gabrielle; Mooney, Mary; O'Brien, Frances; Moser, Debra K
2014-04-01
Patient decision delay is the main reason why many patients fail to receive timely medical intervention for symptoms of acute coronary syndrome (ACS). This study examines the validity of slow-onset and fast-onset ACS presentations and their influence on ACS prehospital delay times. A fast-onset ACS presentation is characterized by sudden, continuous, and severe chest pain, and slow-onset ACS pertains to all other ACS presentations. Baseline data pertaining to medical profiles, prehospital delay times, and ACS symptoms were recorded for all ACS patients who participated in a large multisite randomized control trial (RCT) in Dublin, Ireland. Patients were interviewed 2-4 days after their ACS event, and data were gathered using the ACS Response to Symptom Index. Only baseline data from the RCT, N = 893 patients, were analyzed. A total of 65% (n = 577) of patients experienced slow-onset ACS presentation, whereas 35% (n = 316) experienced fast-onset ACS. Patients who experienced slow-onset ACS were significantly more likely to have longer prehospital delays than patients with fast-onset ACS (3.5 h vs. 2.0 h, respectively, t = -5.63, df 890, p < 0.001). A multivariate analysis of delay revealed that, in the presence of other known delay factors, the only independent predictors of delay were slow-onset and fast-onset ACS (β = -.096, p < 0.002) and other factors associated with patient behavior. Slow-onset ACS and fast-onset ACS presentations are associated with distinct behavioral patterns that significantly influence prehospital time frames. As such, slow-onset ACS and fast-onset ACS are legitimate ACS presentation phenomena that should be seriously considered when examining the factors associated with prehospital delay. Copyright © 2014 Elsevier Inc. All rights reserved.
NASA Astrophysics Data System (ADS)
Kodama, Kazuto
2015-02-01
This study proposes a new method for measuring transient magnetization of natural samples induced by a pulsed field with duration of 11 ms using a pulse magnetizer. An experimental system was constructed, consisting of a pair of differential sensing coils connected with a high-speed digital oscilloscope for data acquisition. The data were transferred to a computer to obtain an initial magnetization curve and a descending branch of a hysteresis loop in a rapidly changing positive field. This system was tested with synthetic samples (permalloy ribbon, aluminum plate, and nickel powder) as well as two volcanic rock samples. Results from the synthetic samples showed considerable differences from those measured by a quasi-static method using a vibrating sample magnetometer (VSM). These differences were principally due to the time-dependent magnetic properties or to electromagnetic effects, such as magnetic viscosity, eddy current loss, or magnetic relaxation. Results from the natural samples showed that the transient magnetization-field curves were largely comparable to the corresponding portions of the hysteresis loops. However, the relative magnetization (scaled to the saturation magnetization) at the end of a pulse was greater than that measured by a VSM. This discrepancy, together with the occurrence of rapid exponential decay after a pulse, indicates magnetic relaxations that could be interpreted in terms of domain wall displacement. These results suggest that with further developments, the proposed technique can become a useful tool for characterizing magnetic particles contained in a variety of natural materials.
NASA Astrophysics Data System (ADS)
Karolak, Aleksandra; Khabibullin, Artem; Budzevich, Mikalai; Martinez, M.; Doliganski, Michael; McLaughlin, Mark; Woods, Lilia; Morse, David
Ligand structures encapsulating metal ions play a central role as contrast agents in Magnetic Resonance Imaging (MRI) or as agents delivering toxic cargo directly to tumor cells in targeted cancer therapy. The structural stability and interaction with solutions of such complexes are the key elements in understanding the foundation of delivery process. We present a comparative study for the 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelated to radioactive isotopes of 225Ac, 221Fr, 217At, 213Bi and a control 68Gd. Using density functional theory methods we investigate the structural stability of complexes for cancer therapy including binding energies, charge transfer, electron densities. The van der Waals interactions are included in the simulations to take into account weak dispersion forces present in such structures. Our results reveal that Ac-DOTA, Bi-DOTA and Gd-DOTA are the most stable complexes in the group. We also show that the water environment is a key ingredient for the structural coordination of the DOTA structures. Support from the US Department of Energy under Grant No. DE-FG02-06ER46297 is acknowledged.
Improved methods for the measurement and analysis of stellar magnetic fields
NASA Technical Reports Server (NTRS)
Saar, Steven H.
1988-01-01
The paper presents several improved methods for the measurement of magnetic fields on cool stars which take into account simple radiative transfer effects and the exact Zeeman patterns. Using these methods, high-resolution, low-noise data can be fitted with theoretical line profiles to determine the mean magnetic field strength in stellar active regions and a model-dependent fraction of the stellar surface (filling factor) covered by these regions. Random errors in the derived field strength and filling factor are parameterized in terms of signal-to-noise ratio, wavelength, spectral resolution, stellar rotation rate, and the magnetic parameters themselves. Weak line blends, if left uncorrected, can have significant systematic effects on the derived magnetic parameters, and thus several methods are developed to compensate partially for them. The magnetic parameters determined by previous methods likely have systematic errors because of such line blends and because of line saturation effects. Other sources of systematic error are explored in detail. These sources of error currently make it difficult to determine the magnetic parameters of individual stars to better than about + or - 20 percent.
Transient AC voltage related phenomena for HVDC schemes connected to weak AC systems
DOE Office of Scientific and Technical Information (OSTI.GOV)
Pilotto, L.A.S.; Szechtman, M.; Hammad, A.E.
1992-07-01
In this paper a didactic explanation of voltage stability associated phenomena at HVDC terminals is presented. Conditions leading to ac voltage collapse problems are identified. A mechanism that excites control-induced voltage oscillations is shown. The voltage stability factor is used for obtaining the maximum power limits of ac/dc systems operating with different control strategies. Correlation to Pd {times} Id curves is given. Solutions for eliminating the risks of voltage collapse and for avoiding control-induced oscillations are discussed. The results are supported by detailed digital simulations of a weak ac/dc system using EMTP.
Magnetic agglomeration method for size control in the synthesis of magnetic nanoparticles
Huber, Dale L [Albuquerque, NM
2011-07-05
A method for controlling the size of chemically synthesized magnetic nanoparticles that employs magnetic interaction between particles to control particle size and does not rely on conventional kinetic control of the reaction to control particle size. The particles are caused to reversibly agglomerate and precipitate from solution; the size at which this occurs can be well controlled to provide a very narrow particle size distribution. The size of particles is controllable by the size of the surfactant employed in the process; controlling the size of the surfactant allows magnetic control of the agglomeration and precipitation processes. Agglomeration is used to effectively stop particle growth to provide a very narrow range of particle sizes.
Method and apparatus for using magneto-acoustic remanence to determine embrittlement
NASA Technical Reports Server (NTRS)
Allison, Sidney G. (Inventor); Namkung, Min (Inventor); Yost, William T. (Inventor); Cantrell, John H. (Inventor)
1992-01-01
A method and apparatus for testing steel components for temperature embrittlement uses magneto-acoustic emission to nondestructively evaluate the component are presented. Acoustic emission signals occur more frequently at higher levels in embrittled components. A pair of electromagnets are used to create magnetic induction in the test component. Magneto-acoustic emission signals may be generated by applying an AC current to the electromagnets. The acoustic emission signals are analyzed to provide a comparison between a component known to be unembrittled and a test component. Magnetic remanence is determined by applying a DC current to the electromagnets and then by turning the magnets off and observing the residual magnetic induction.
Determination of ac conductor and pipe loss in pipe-type cable systems. Final report
DOE Office of Scientific and Technical Information (OSTI.GOV)
Silver, D.A.; Seman, G.W.
1982-02-01
The results are presented of investigations into the determination of the ac/dc resistance ratios of high and extra high voltage pipe-type cables with conventional and large size segmental conductors in carbon steel, stainless steel and aluminum pipes in three cable per pipe and single cable per pipe configurations. The measurements included 115 through 765 kV cables with copper, enamel coated copper, and aluminum conductors in sizes of 2000 kcmil (1015 mm/sup 2/), 3250 kcmil (1650 mm/sup 2/), and 3500 kcmil (1776 mm/sup 2/). Calculations using presently available techniques were employed to provide correlation between measured and calculated values in bothmore » magnetic and non-magnetic pipes. In addition, a number of new techniques in conductor construction, pipe material and pipe liners and cable wraps were investigated as means of decreasing the ac/dc resistance ratios of pipe-type cables. Finally, the various systems studied were compared on the basis of system MVA rating and by evaluation of installed and overall operating costs as compared to conventional three cable per pipe systems installed in carbon steel pipes.« less
Method and apparatus for assembling permanent magnet rotors
Hsu, John S.; Adams, Donald J.
1999-01-01
A permanent magnet assembly (22) for assembly in large permanent magnet (PM) motors and generators includes a two-piece carrier (23, 24) that can be slid into a slot (13) in the rotor (10) and then secured in place using a set screw (37). The invention also provides an auxiliary carrier device (50) with guide rails (51) that line up with the teeth (12) of the rotor, so that a permanent magnet assembly (22) can be pushed first into a slot (13), and then down the slot (13) to its proper location. An auxiliary tool (50) is provided to move the permanent magnet assembly (22) into position in the slot (13) before it is secured in place. Methods of assembling and disassembling the magnet assemblies (22) in the rotor (10) are also disclosed.
NASA Astrophysics Data System (ADS)
Dutta, Papia; Mandal, S. K.; Nath, A.
2018-05-01
Nanocrystalline BaFe2O4 has been prepared through low temperature pyrophoric reaction method. The structural, dielectric and electrical transport properties of BaFe2O4 are investigated in detail. AC electrical properties have been studied over the wide range of frequencies with applied dc magnetic fields and temperatures. The value of impedance is found to increase with increase in magnetic field attributing the magnetostriction property of the sample. The observed value of magneto-impedance and magnetodielectric is found to ∼32% and ∼33% at room temperature. Nyquist plots have been fitted using resistance-capacitor circuits at different magnetic fields and temperatures showing the dominant role of grain and grain boundaries of the sample. Metal-semiconductor transition ∼403 K has been discussed in terms of delocalized and localized charge carrier.We have estimated activation energy using Arrhenius relation indicating temperature dependent electrical relaxation process in the system. Ac conductivity follow a Jonscher’s single power law indicating the large and small polaronic hopping conduction mechanism in the system.
Microfabricated AC impedance sensor
Krulevitch, Peter; Ackler, Harold D.; Becker, Frederick; Boser, Bernhard E.; Eldredge, Adam B.; Fuller, Christopher K.; Gascoyne, Peter R. C.; Hamilton, Julie K.; Swierkowski, Stefan P.; Wang, Xiao-Bo
2002-01-01
A microfabricated instrument for detecting and identifying cells and other particles based on alternating current (AC) impedance measurements. The microfabricated AC impedance sensor includes two critical elements: 1) a microfluidic chip, preferably of glass substrates, having at least one microchannel therein and with electrodes patterned on both substrates, and 2) electrical circuits that connect to the electrodes on the microfluidic chip and detect signals associated with particles traveling down the microchannels. These circuits enable multiple AC impedance measurements of individual particles at high throughput rates with sufficient resolution to identify different particle and cell types as appropriate for environmental detection and clinical diagnostic applications.
NASA Astrophysics Data System (ADS)
Kondo, T.; Mori, K.; Hachisu, M.; Yamazaki, T.; Okamoto, D.; Watanabe, M.; Gonda, K.; Tada, H.; Hamada, Y.; Takano, M.; Ohuchi, N.; Ichiyanagi, Y.
2015-05-01
Mn-Zn ferrite, Mn1-xZnxFe2O4 nanoparticles encapsulated in amorphous SiO2 were prepared using our original wet chemical method. X-ray diffraction patterns confirmed that the diameters of these particles were within 7-30 nm. Magnetization measurements for various sample compositions revealed that the saturation magnetization (Ms) of 7 nm particles was maximum for the x = 0.2 sample. AC magnetic susceptibility measurements were performed for Mn0.8Zn0.2Fe2O4 (x = 0.2) samples with 13-30 nm particles. The peak of the imaginary part of the magnetic susceptibility χ″ shifted to higher temperatures as the particle size increased. An AC field was found to cause the increase in temperature, with the 18 nm particles exhibiting the highest temperature increase, as expected. In addition, in vitro experiments were carried out to study the hyperthermia effects of Mn1-xZnxFe2O4 (x = 0.2, 18 nm) particles on human cancer cells.
Methods for making radially anisotropic thin-film magnetic torroidal cores
DOE Office of Scientific and Technical Information (OSTI.GOV)
Qiu, Jizheng; Sullivan, Charles R.
2017-05-23
A method of forming a radially anisotropic toroidal magnetic core includes providing apparatus having a first magnet for providing a radial magnetic field extending across a cavity from an axial spindle to a surrounding second magnetic element, placing a substrate in the cavity, the substrate having a hole fitting around the head of the spindle; and sputter-depositing a film of ferromagnetic material onto the substrate. In an embodiment, the spindle is magnetically coupled to a first pole of the first magnet, the second magnetic element is coupled to a second pole of the first magnet, and a thermally conductive, nonmagnetic,more » insert separates the spindle and the second magnetic element.« less
Study of magnetic bearings with high temperature superconductors, phase 3
NASA Technical Reports Server (NTRS)
Eyssa, Y. M.; Huang, X.
1991-01-01
Three areas related to the actively controlled radial magnetic bearing concepts are discussed. These areas are: (1) modification to the ac loss calculations of the 1990 report; (2) a continuous changing mechanism to compensate rotor current drop due to ac losses; and (3) design of a proof of principle experiment simulating the proposed bearing concept.
Research on key technology of planning and design for AC/DC hybrid distribution network
NASA Astrophysics Data System (ADS)
Shen, Yu; Wu, Guilian; Zheng, Huan; Deng, Junpeng; Shi, Pengjia
2018-04-01
With the increasing demand of DC generation and DC load, the development of DC technology, AC and DC distribution network integrating will become an important form of future distribution network. In this paper, the key technology of planning and design for AC/DC hybrid distribution network is proposed, including the selection of AC and DC voltage series, the design of typical grid structure and the comprehensive evaluation method of planning scheme. The research results provide some ideas and directions for the future development of AC/DC hybrid distribution network.
NASA Astrophysics Data System (ADS)
Abbas, Qamar; Béguin, François
2016-06-01
We demonstrate that an activated carbon (AC)-based electrochemical capacitor implementing aqueous lithium sulfate electrolyte in 7:3 vol:vol water/methanol mixture can operate down to -40 °C with good electrochemical performance. Three-electrode cell investigations show that the faradaic contributions related with hydrogen chemisorption in the negative AC electrode are thermodynamically unfavored at -40 °C, enabling the system to work as a typical electrical double-layer (EDL) capacitor. After prolonged floating of the AC/AC capacitor at 1.6 V and -40°C, the capacitance, equivalent series resistance and efficiency remain constant, demonstrating the absence of ageing related with side redox reactions at this temperature. Interestingly, when temperature is increased back to 24 °C, the redox behavior due to hydrogen storage reappears and the system behaves as a freshly prepared one.
Rovina, Kobun; Siddiquee, Shafiquzzaman; Shaarani, Sharifudin M
2016-01-01
Allura Red AC (E129) is an azo dye that widely used in drinks, juices, bakery, meat, and sweets products. High consumption of Allura Red has claimed an adverse effects of human health including allergies, food intolerance, cancer, multiple sclerosis, attention deficit hyperactivity disorder, brain damage, nausea, cardiac disease and asthma due to the reaction of aromatic azo compounds (R = R' = aromatic). Several countries have banned and strictly controlled the uses of Allura Red in food and beverage products. This review paper is critically summarized on the available analytical and advanced methods for determination of Allura Red and also concisely discussed on the acceptable daily intake, toxicology and extraction methods.
Superconducting magnetic energy storage for asynchronous electrical systems
Boenig, H.J.
1984-05-16
It is an object of the present invention to provide superconducting magnetic energy storage for a plurality of asynchronous electrical systems. It is a further object of the present invention to provide load leveling and stability improvement in a plurality of independent ac systems using a single superconducting magnetic energy storage coil.
Hybrid-secondary uncluttered permanent magnet machine and method
Hsu, John S.
2005-12-20
An electric machine (40) has a stator (43), a permanent magnet rotor (38) with permanent magnets (39) and a magnetic coupling uncluttered rotor (46) for inducing a slip energy current in secondary coils (47). A dc flux can be produced in the uncluttered rotor when the secondary coils are fed with dc currents. The magnetic coupling uncluttered rotor (46) has magnetic brushes (A, B, C, D) which couple flux in through the rotor (46) to the secondary coils (47c, 47d) without inducing a current in the rotor (46) and without coupling a stator rotational energy component to the secondary coils (47c, 47d). The machine can be operated as a motor or a generator in multi-phase or single-phase embodiments and is applicable to the hybrid electric vehicle. A method of providing a slip energy controller is also disclosed.
21 CFR 886.1630 - AC-powered photostimulator.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false AC-powered photostimulator. 886.1630 Section 886.1630 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED... allows measurement of retinal or visual function by perceptual or electrical methods (e.g., stroboscope...
NASA Astrophysics Data System (ADS)
Jorge, Guillermo A.; Llera, María; Bekeris, Victoria
2017-12-01
We study the propulsion of superparamagnetic particles dispersed in a viscous fluid upon the application of an elliptically polarized rotating magnetic field. Reducing the fluid surface tension the particles sediment due to density mismatch and rotate close to the low recipient confining plate. We study the net translational motion arising from the hydrodynamic coupling with the plate and find that, above a cross over magnetic field, magnetically assembled doublets move faster than single particles. In turn, particles are driven in complex highly controlled trajectories by rotating the plane containing the magnetic field vector. The effect of the field rotation on long self assembled chains is discussed and the alternating breakup and reformation of the particle chains is described.
Makridis, A; Chatzitheodorou, I; Topouridou, K; Yavropoulou, M P; Angelakeris, M; Dendrinou-Samara, C
2016-06-01
The application of ferrite magnetic nanoparticles (MNPs) in medicine finds its rapidly developing emphasis on heating mediators for magnetic hyperthermia, the ever-promising "fourth leg" of cancer treatment. Usage of MNPs depends largely on the preparation processes to select optimal conditions and effective routes to finely tailor MNPs. Microwave heating, instead of conventional heating offers nanocrystals at significantly enhanced rate and yield. In this work, a facile mass-production microwave hydrothermal synthetic approach was used to synthesize stable ferromagnetic manganese and cobalt ferrite nanoparticles with sizes smaller than 14 nm from metal acetylacetonates in the presence of octadecylamine. Prolonging the reaction time from 15 to 60 min, led to ferrites with improved crystallinity while the sizes are slight increased. The high crystallinity magnetic nanoparticles showed exceptional magnetic heating parameters. In vitro application was performed using the human osteosarcoma cell line Saos-2 incubated with manganese ferrite nanoparticles. Hyperthermia applied in a two cycle process, while AC magnetic field remained on until the upper limit of 45 °C was achieved. The comparative results of the AC hyperthermia efficiency of ferrite nanoparticles in combination with the in vitro study coincide with the magnetic features and their tunability may be further exploited for AC magnetic hyperthermia driven applications. Copyright © 2016 Elsevier B.V. All rights reserved.
Magnetic properties in polycrystalline and single crystal Ca-doped LaCoO3
NASA Astrophysics Data System (ADS)
Zeng, R.; Debnath, J. C.; Chen, D. P.; Shamba, P.; Wang, J. L.; Kennedy, S. J.; Campbell, S. J.; Silver, T.; Dou, S. X.
2011-04-01
Polycrystalline (PC) and single crystalline (SC) Ca-doped LaCoO3 (LCCO) samples with the perovskite structure were synthesized by conventional solid-state reaction and the floating-zone growth method. We present the results of a comprehensive investigation of the magnetic properties of the LCCO system. Systematic measurements have been conducted on dc magnetization, ac susceptibility, exchange-bias, and the magnetocaloric effect. These findings suggest that complex structural phases, ferromagnetic (FM), and spin-glass/cluster-spin-glass (CSG), and their transitions exist in PC samples, while there is a much simpler magnetic phase in SC samples. It was also of interest to discover that the CSG induced a magnetic field memory effect and an exchange-bias-like effect, and that a large inverse irreversible magnetocaloric effect exists in this system.
AC losses in horizontally parallel HTS tapes for possible wireless power transfer applications
NASA Astrophysics Data System (ADS)
Shen, Boyang; Geng, Jianzhao; Zhang, Xiuchang; Fu, Lin; Li, Chao; Zhang, Heng; Dong, Qihuan; Ma, Jun; Gawith, James; Coombs, T. A.
2017-12-01
This paper presents the concept of using horizontally parallel HTS tapes with AC loss study, and the investigation on possible wireless power transfer (WPT) applications. An example of three parallel HTS tapes was proposed, whose AC loss study was carried out both from experiment using electrical method; and simulation using 2D H-formulation on the FEM platform of COMSOL Multiphysics. The electromagnetic induction around the three parallel tapes was monitored using COMSOL simulation. The electromagnetic induction and AC losses generated by a conventional three turn coil was simulated as well, and then compared to the case of three parallel tapes with the same AC transport current. The analysis demonstrates that HTS parallel tapes could be potentially used into wireless power transfer systems, which could have lower total AC losses than conventional HTS coils.
System and method for magnetic current density imaging at ultra low magnetic fields
Espy, Michelle A.; George, John Stevens; Kraus, Robert Henry; Magnelind, Per; Matlashov, Andrei Nikolaevich; Tucker, Don; Turovets, Sergei; Volegov, Petr Lvovich
2016-02-09
Preferred systems can include an electrical impedance tomography apparatus electrically connectable to an object; an ultra low field magnetic resonance imaging apparatus including a plurality of field directions and disposable about the object; a controller connected to the ultra low field magnetic resonance imaging apparatus and configured to implement a sequencing of one or more ultra low magnetic fields substantially along one or more of the plurality of field directions; and a display connected to the controller, and wherein the controller is further configured to reconstruct a displayable image of an electrical current density in the object. Preferred methods, apparatuses, and computer program products are also disclosed.
Biasing and fast degaussing circuit for magnetic materials
Dress, Jr., William B.; McNeilly, David R.
1984-01-01
A dual-function circuit is provided which may be used to both magnetically bias and alternately, quickly degauss a magnetic device. The circuit may be magnetically coupled or directly connected electrically to a magnetic device, such as a magnetostrictive transducer, to magnetically bias the device by applying a d.c. current and alternately apply a selectively damped a.c. current to the device to degauss the device. The circuit is of particular value in many systems which use magnetostrictive transducers for ultrasonic transmission in different propagation modes over very short time periods.
Biasing and fast degaussing circuit for magnetic materials
Dress, W.B. Jr.; McNeilly, D.R.
1983-10-04
A dual-function circuit is provided which may be used to both magnetically bias and alternately, quickly degauss a magnetic device. The circuit may be magnetically coupled or directly connected electrically to a magnetic device, such as a magnetostrictive transducer, to magnetically bias the device by applying a dc current and alternately apply a selectively damped ac current to the device to degauss the device. The circuit is of particular value in many systems which use magnetostrictive transducers for ultrasonic transmission in different propagation modes over very short time periods.
Monte Carlo method for magnetic impurities in metals
NASA Technical Reports Server (NTRS)
Hirsch, J. E.; Fye, R. M.
1986-01-01
The paper discusses a Monte Carlo algorithm to study properties of dilute magnetic alloys; the method can treat a small number of magnetic impurities interacting wiith the conduction electrons in a metal. Results for the susceptibility of a single Anderson impurity in the symmetric case show the expected universal behavior at low temperatures. Some results for two Anderson impurities are also discussed.
Frequent statistics of link-layer bit stream data based on AC-IM algorithm
NASA Astrophysics Data System (ADS)
Cao, Chenghong; Lei, Yingke; Xu, Yiming
2017-08-01
At present, there are many relevant researches on data processing using classical pattern matching and its improved algorithm, but few researches on statistical data of link-layer bit stream. This paper adopts a frequent statistical method of link-layer bit stream data based on AC-IM algorithm for classical multi-pattern matching algorithms such as AC algorithm has high computational complexity, low efficiency and it cannot be applied to binary bit stream data. The method's maximum jump distance of the mode tree is length of the shortest mode string plus 3 in case of no missing? In this paper, theoretical analysis is made on the principle of algorithm construction firstly, and then the experimental results show that the algorithm can adapt to the binary bit stream data environment and extract the frequent sequence more accurately, the effect is obvious. Meanwhile, comparing with the classical AC algorithm and other improved algorithms, AC-IM algorithm has a greater maximum jump distance and less time-consuming.
Methods for Probing Magnetic Films with Neutrons
NASA Astrophysics Data System (ADS)
Kozhevnikov, S. V.; Ott, F.; Radu, F.
2018-03-01
We review various methods in the investigation of magnetic films with neutrons, including those based on the effects of Larmor precession, Zeeman spatial splitting of the beam, neutron spin resonance, and polarized neutron channeling. The underlying principles, examples of the investigated systems, specific features, applications, and perspectives of these methods are discussed.
Soft x-ray coherent diffraction imaging on magnetic nanostructures
NASA Astrophysics Data System (ADS)
Shi, Xiaowen; Lee, James; Mishra, Shrawan; Parks, Daniel; Tyliszczak, Tolek; Shapiro, David; Roy, Sujoy; Kevan, Steve; Stxm Team At Als Collaboration; Soft X-Ray Microscopy Group At Als Collaboration; Soft X-ray scattering at ALS, LBL Team
2014-03-01
Coherent soft X-rays diffraction imaging enable coherent magnetic resonance scattering at transition metal L-edge to be probed so that magnetic domains could be imaged with very high spatial resolution with phase contrast, reaching sub-10nm. One of the overwhelming advantages of using coherent X-rays is the ability to resolve phase contrast images with linearly polarized light with both phase and absorption contrast comparing to real-space imaging, which can only be studied with circularly polarized light with absorption contrast only. Here we report our first results on high-resolution of magnetic domains imaging of CoPd multilayer thin film with coherent soft X-ray ptychography method. We are aiming to resolve and understand magnetic domain wall structures with the highest obtainable resolution here at Advanced Light Source. In principle types of magnetic domain walls could be studied so that Neel or Bloch walls can be distinguished by imaging. This work at LBNL was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy (contract no. DE-AC02- 05CH11231).
HOT PLASMA FROM SOLAR ACTIVE REGION CORES: A TEST OF AC AND DC CORONAL HEATING MODELS?
DOE Office of Scientific and Technical Information (OSTI.GOV)
Schmelz, J. T.; Christian, G. M.; Dhaliwal, R. S.
2015-06-20
Direct current (DC) models of solar coronal heating invoke magnetic reconnection to convert magnetic free energy into heat, whereas alternating current (AC) models invoke wave dissipation. In both cases the energy is supplied by photospheric footpoint motions. For a given footpoint velocity amplitude, DC models predict lower average heating rates but greater temperature variability when compared to AC models. Therefore, evidence of hot plasma (T > 5 MK) in the cores of active regions could be one of the ways for current observations to distinguish between AC and DC models. We have analyzed data from the X-Ray Telescope (XRT) andmore » the Atmospheric Imaging Assembly for 12 quiescent active region cores, all of which were observed in the XRT Be-thick channel. We did Differential Emission Measure (DEM) analysis and achieved good fits for each data set. We then artificially truncated the hot plasma of the DEM model at 5 MK and examined the resulting fits to the data. For some regions in our sample, the XRT intensities continued to be well-matched by the DEM predictions, even without the hot plasma. This truncation, however, resulted in unacceptable fits for the other regions. This result indicates that the hot plasma is present in these regions, even if the precise DEM distribution cannot be determined with the data available. We conclude that reconnection may be heating the hot plasma component of these active regions.« less
The magnetofection method: using magnetic force to enhance gene delivery.
Plank, Christian; Schillinger, Ulrike; Scherer, Franz; Bergemann, Christian; Rémy, Jean-Serge; Krötz, Florian; Anton, Martina; Lausier, Jim; Rosenecker, Joseph
2003-05-01
In order to enhance and target gene delivery we have previously established a novel method, termed magnetofection, which uses magnetic force acting on gene vectors that are associated with magnetic particles. Here we review the benefits, the mechanism and the potential of the method with regard to overcoming physical limitations to gene delivery. Magnetic particle chemistry and physics are discussed, followed by a detailed presentation of vector formulation and optimization work. While magnetofection does not necessarily improve the overall performance of any given standard gene transfer method in vitro, its major potential lies in the extraordinarily rapid and efficient transfection at low vector doses and the possibility of remotely controlled vector targeting in vivo.
Guo, Jiang; Kum, Chun Wai; Au, Ka Hing; Tan, Zhi'En Eddie; Wu, Hu; Liu, Kui
2016-06-13
In order to polish microstructured surface without deteriorating its profile, we propose a new vibration-assisted magnetic abrasive polishing (VAMAP) method. In this method, magnetic force guarantees that the magnetic abrasives can well contact the microstructured surface and access the corners of microstructures while vibration produces a relative movement between microstructures and magnetic abrasives. As the vibration direction is parallel to the microstructures, the profile of the microstructures will not be deteriorated. The relation between vibration and magnetic force was analyzed and the feasibility of this method was experimentally verified. The results show that after polishing, the surface finish around microstructures was significantly improved while the profile of microstructures was well maintained.
Combined AC electroosmosis and dielectrophoresis for controlled rotation of microparticles
Walid Rezanoor, Md.; Dutta, Prashanta
2016-01-01
Electrorotation is widely used for characterization of biological cells and materials using a rotating electric field. Generally, multiphase AC electric fields and quadrupolar electrode configuration are needed to create a rotating electric field for electrorotation. In this study, we demonstrate a simple method to rotate dielectrophoretically trapped microparticles using a stationary AC electric field. Coplanar interdigitated electrodes are used to create a linearly polarized nonuniform AC electric field. This nonuniform electric field is employed for dielectrophoretic trapping of microparticles as well as for generating electroosmotic flow in the vicinity of the electrodes resulting in rotation of microparticles in a microfluidic device. The rotation of barium titanate microparticles is observed in 2-propanol and methanol solvent at a frequency below 1 kHz. A particle rotation rate as high as 240 revolutions per minute is observed. It is demonstrated that precise manipulation (both rotation rate and equilibrium position) of the particles is possible by controlling the frequency of the applied electric field. At low frequency range, the equilibrium positions of the microparticles are observed between the electrode edge and electrode center. This method of particle manipulation is different from electrorotation as it uses induced AC electroosmosis instead of electric torque as in the case of electrorotation. Moreover, it has been shown that a microparticle can be rotated along its own axis without any translational motion. PMID:27014394
Combined AC electroosmosis and dielectrophoresis for controlled rotation of microparticles.
Walid Rezanoor, Md; Dutta, Prashanta
2016-03-01
Electrorotation is widely used for characterization of biological cells and materials using a rotating electric field. Generally, multiphase AC electric fields and quadrupolar electrode configuration are needed to create a rotating electric field for electrorotation. In this study, we demonstrate a simple method to rotate dielectrophoretically trapped microparticles using a stationary AC electric field. Coplanar interdigitated electrodes are used to create a linearly polarized nonuniform AC electric field. This nonuniform electric field is employed for dielectrophoretic trapping of microparticles as well as for generating electroosmotic flow in the vicinity of the electrodes resulting in rotation of microparticles in a microfluidic device. The rotation of barium titanate microparticles is observed in 2-propanol and methanol solvent at a frequency below 1 kHz. A particle rotation rate as high as 240 revolutions per minute is observed. It is demonstrated that precise manipulation (both rotation rate and equilibrium position) of the particles is possible by controlling the frequency of the applied electric field. At low frequency range, the equilibrium positions of the microparticles are observed between the electrode edge and electrode center. This method of particle manipulation is different from electrorotation as it uses induced AC electroosmosis instead of electric torque as in the case of electrorotation. Moreover, it has been shown that a microparticle can be rotated along its own axis without any translational motion.
Toroidal-Core Microinductors Biased by Permanent Magnets
NASA Technical Reports Server (NTRS)
Lieneweg, Udo; Blaes, Brent
2003-01-01
The designs of microscopic toroidal-core inductors in integrated circuits of DC-to-DC voltage converters would be modified, according to a proposal, by filling the gaps in the cores with permanent magnets that would apply bias fluxes (see figure). The magnitudes and polarities of the bias fluxes would be tailored to counteract the DC fluxes generated by the DC components of the currents in the inductor windings, such that it would be possible to either reduce the sizes of the cores or increase the AC components of the currents in the cores without incurring adverse effects. Reducing the sizes of the cores could save significant amounts of space on integrated circuits because relative to other integrated-circuit components, microinductors occupy large areas - of the order of a square millimeter each. An important consideration in the design of such an inductor is preventing magnetic saturation of the core at current levels up to the maximum anticipated operating current. The requirement to prevent saturation, as well as other requirements and constraints upon the design of the core are expressed by several equations based on the traditional magnetic-circuit approximation. The equations involve the core and gap dimensions and the magnetic-property parameters of the core and magnet materials. The equations show that, other things remaining equal, as the maximum current is increased, one must increase the size of the core to prevent the flux density from rising to the saturation level. By using a permanent bias flux to oppose the flux generated by the DC component of the current, one would reduce the net DC component of flux in the core, making it possible to reduce the core size needed to prevent the total flux density (sum of DC and AC components) from rising to the saturation level. Alternatively, one could take advantage of the reduction of the net DC component of flux by increasing the allowable AC component of flux and the corresponding AC component of current
Dielectric breakdown strength of magnetic nanofluid based on insulation oil after impulse test
NASA Astrophysics Data System (ADS)
Nazari, M.; Rasoulifard, M. H.; Hosseini, H.
2016-02-01
In this study, the dielectric breakdown strength of magnetic nanofluids based on transformer mineral oil for use in power systems is reviewed. Nano oil samples are obtained from dispersion of the magnetic nanofluid within uninhibited transformer mineral oil NYTRO LIBRA as the base fluid. AC dielectric breakdown voltage measurement was carried out according to IEC 60156 standard and the lightning impulse breakdown voltage was obtained by using the sphere-sphere electrodes in an experimental setup for nano oil in volume concentration of 0.1-0.6%. Results indicate improved AC and lightning impulse breakdown voltage of nano oil compared to the base oil. AC test was performed again after applying impulse current and result showed that nano oil unlike the base oil retains its dielectric properties. Increase the dielectric strength of the nano oil is mainly due to dielectric and magnetic properties of Fe3O4 nanoparticles that act as free electrons snapper, and reduce the rate of free electrons in the ionization process.
Imaging of dynamic magnetic fields with spin-polarized neutron beams
Tremsin, A. S.; Kardjilov, N.; Strobl, M.; ...
2015-04-22
Precession of neutron spin in a magnetic field can be used for mapping of a magnetic field distribution, as demonstrated previously for static magnetic fields at neutron beamline facilities. The fringing in the observed neutron images depends on both the magnetic field strength and the neutron energy. In this paper we demonstrate the feasibility of imaging periodic dynamic magnetic fields using a spin-polarized cold neutron beam. Our position-sensitive neutron counting detector, providing with high precision both the arrival time and position for each detected neutron, enables simultaneous imaging of multiple phases of a periodic dynamic process with microsecond timing resolution.more » The magnetic fields produced by 5- and 15-loop solenoid coils of 1 cm diameter, are imaged in our experiments with ~100 μm resolution for both dc and 3 kHz ac currents. Our measurements agree well with theoretical predictions of fringe patterns formed by neutron spin precession. We also discuss the wavelength dependence and magnetic field quantification options using a pulsed neutron beamline. Furthermore, the ability to remotely map dynamic magnetic fields combined with the unique capability of neutrons to penetrate various materials (e.g., metals), enables studies of fast periodically changing magnetic processes, such as formation of magnetic domains within metals due to the presence of ac magnetic fields.« less
Imaging of dynamic magnetic fields with spin-polarized neutron beams
DOE Office of Scientific and Technical Information (OSTI.GOV)
Tremsin, A. S.; Kardjilov, N.; Strobl, M.
Precession of neutron spin in a magnetic field can be used for mapping of a magnetic field distribution, as demonstrated previously for static magnetic fields at neutron beamline facilities. The fringing in the observed neutron images depends on both the magnetic field strength and the neutron energy. In this paper we demonstrate the feasibility of imaging periodic dynamic magnetic fields using a spin-polarized cold neutron beam. Our position-sensitive neutron counting detector, providing with high precision both the arrival time and position for each detected neutron, enables simultaneous imaging of multiple phases of a periodic dynamic process with microsecond timing resolution.more » The magnetic fields produced by 5- and 15-loop solenoid coils of 1 cm diameter, are imaged in our experiments with ~100 μm resolution for both dc and 3 kHz ac currents. Our measurements agree well with theoretical predictions of fringe patterns formed by neutron spin precession. We also discuss the wavelength dependence and magnetic field quantification options using a pulsed neutron beamline. Furthermore, the ability to remotely map dynamic magnetic fields combined with the unique capability of neutrons to penetrate various materials (e.g., metals), enables studies of fast periodically changing magnetic processes, such as formation of magnetic domains within metals due to the presence of ac magnetic fields.« less
Roesler, Alexander W [Tijeras, NM; Christenson, Todd R [Albuquerque, NM
2007-04-24
Methods are provided for forming a plurality of permanent magnets with two different north-south magnetic pole alignments for use in microelectromechanical (MEM) devices. These methods are based on initially magnetizing the permanent magnets all in the same direction, and then utilizing a combination of heating and a magnetic field to switch the polarity of a portion of the permanent magnets while not switching the remaining permanent magnets. The permanent magnets, in some instances, can all have the same rare-earth composition (e.g. NdFeB) or can be formed of two different rare-earth materials (e.g. NdFeB and SmCo). The methods can be used to form a plurality of permanent magnets side-by-side on or within a substrate with an alternating polarity, or to form a two-dimensional array of permanent magnets in which the polarity of every other row of the array is alternated.
Development of a Magnetic Attachment Method for Bionic Eye Applications.
Fox, Kate; Meffin, Hamish; Burns, Owen; Abbott, Carla J; Allen, Penelope J; Opie, Nicholas L; McGowan, Ceara; Yeoh, Jonathan; Ahnood, Arman; Luu, Chi D; Cicione, Rosemary; Saunders, Alexia L; McPhedran, Michelle; Cardamone, Lisa; Villalobos, Joel; Garrett, David J; Nayagam, David A X; Apollo, Nicholas V; Ganesan, Kumaravelu; Shivdasani, Mohit N; Stacey, Alastair; Escudie, Mathilde; Lichter, Samantha; Shepherd, Robert K; Prawer, Steven
2016-03-01
Successful visual prostheses require stable, long-term attachment. Epiretinal prostheses, in particular, require attachment methods to fix the prosthesis onto the retina. The most common method is fixation with a retinal tack; however, tacks cause retinal trauma, and surgical proficiency is important to ensure optimal placement of the prosthesis near the macula. Accordingly, alternate attachment methods are required. In this study, we detail a novel method of magnetic attachment for an epiretinal prosthesis using two prostheses components positioned on opposing sides of the retina. The magnetic attachment technique was piloted in a feline animal model (chronic, nonrecovery implantation). We also detail a new method to reliably control the magnet coupling force using heat. It was found that the force exerted upon the tissue that separates the two components could be minimized as the measured force is proportionately smaller at the working distance. We thus detail, for the first time, a surgical method using customized magnets to position and affix an epiretinal prosthesis on the retina. The position of the epiretinal prosthesis is reliable, and its location on the retina is accurately controlled by the placement of a secondary magnet in the suprachoroidal location. The electrode position above the retina is less than 50 microns at the center of the device, although there were pressure points seen at the two edges due to curvature misalignment. The degree of retinal compression found in this study was unacceptably high; nevertheless, the normal structure of the retina remained intact under the electrodes. Copyright © 2015 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.
Effects of Activated Carbon Surface Property on Structure and Activity of Ru/AC Catalysts
NASA Astrophysics Data System (ADS)
Xu, S. K.; Li, L. M.; Guo, N. N.
2018-05-01
The activated carbon (AC) was modified by supercritical (SC) methanol, HNO3 oxidation, or HNO3 oxidation plus SC methanol, respectively. Then, the original and the modified AC were used as supports for Ru/AC catalysts prepared via the impregnation method. The results showed that the SC methanol modification decreased the content of surface acidic groups of AC. While HNO3 oxidation displayed the opposite behavior. Furthermore, the dispersion of ruthenium and the activity of catalysts were highly dependent on the content of surface acidic groups, and the SC methanol modified sample exhibited the highest activity for hydrogenation of glucose.
Methods for magnetic resonance analysis using magic angle technique
Hu, Jian Zhi [Richland, WA; Wind, Robert A [Kennewick, WA; Minard, Kevin R [Kennewick, WA; Majors, Paul D [Kennewick, WA
2011-11-22
Methods of performing a magnetic resonance analysis of a biological object are disclosed that include placing the object in a main magnetic field (that has a static field direction) and in a radio frequency field; rotating the object at a frequency of less than about 100 Hz around an axis positioned at an angle of about 54.degree.44' relative to the main magnetic static field direction; pulsing the radio frequency to provide a sequence that includes a phase-corrected magic angle turning pulse segment; and collecting data generated by the pulsed radio frequency. In particular embodiments the method includes pulsing the radio frequency to provide at least two of a spatially selective read pulse, a spatially selective phase pulse, and a spatially selective storage pulse. Further disclosed methods provide pulse sequences that provide extended imaging capabilities, such as chemical shift imaging or multiple-voxel data acquisition.
NASA Astrophysics Data System (ADS)
Urban, S. E.; Corbin, T. E.; Wycoff, G. L.; Makarov, V. V.; Høg, E.; Fabricius, C.
2001-12-01
For over 100 years, the international project known as the Astrographic Catalogue -- which involved 20 observatories tasked to photograph the sky -- has held an unfulfilled promised of yielding a wealth of astrometric information. This promise was not realized due to the inadequate reductions of the project's plates. However, in 1997 the U.S. Naval Observatory (USNO) completed the reductions of the 22,660 plates. That catalogue, named the AC 2000, contained positions and magnitudes for 4.6 million stars down to about v magnitude 12.5. Due to the early epochs of the data -- averaging 1907 -- and the positional accuracies -- between 150 and 400 milliarcseconds -- the data are extremely valuable in computing proper motions. In 1997, these positions were used to form the proper motions of the ACT Reference Catalogue. In 1999, USNO and Copenhagen University Observatory (CUO) partnered to create the Tycho-2 Catalogue. The CUO group re-analyzed the data from the Tycho experiment on the Hipparcos satellite. The USNO group re-analyzed over 140 positional catalogs which were combined with the expanded Tycho positions from the CUO group to compute the Tycho-2 proper motions. The largest contributor to these proper motions was the re-analyzed Astrographic Catalogue; the latest version being known as the AC 2000.2 Catalogue. There are two major differences between the AC 2000 and the AC 2000.2. First, the reference catalog used in AC 2000.2 was an expanded version of the Astrographic Catalogue Reference Stars that was rigorously derived on the Hipparcos Celestial Reference Frame. The second is that AC 2000.2 contains photometry from Tycho-2, where available. A description of the AC 2000.2 Catalogue, the reduction techniques used, how it compares with the 1997 version, and information on obtaining the data will be presented.
Magneto-Optic Kerr Effect in a Magnetized Electron Gun
NASA Astrophysics Data System (ADS)
Hardy, Benjamin; Grames, Joseph; CenterInjectors; Sources Team
2016-09-01
Magnetized electron sources have the potential to improve ion beam cooling efficiency. At the Gun Test Stand at Jefferson Lab, a solenoid magnet will be installed adjacent to the photogun to magnetize the electron beam. Due to the photocathode operating in a vacuum chamber, measuring and monitoring the magnetic field at the beam source location with conventional probes is impractical. The Magneto-Optical Kerr Effect (MOKE) describes the change on polarized light by reflection from a magnetized surface. The reflection from the surface may alter the polarization direction, ellipticity, or intensity, and depends linearly upon the surface magnetization of the sample. By replacing the photocathode with a magnetized sample and reflecting polarized light from the sample surface, the magnetic field at the beam source is inferred. A controlled MOKE system has been assembled to test the magnetic field. Calibration of the solenoid magnet is performed by comparing the MOKE signal with magnetic field measurements. The apparatus will provide a description of the field at electron beam source. The report summarizes the method and results of controlled tests and calibration of the MOKE sample with the solenoid magnet field measurements. This work is supported by the National Science Foundation, Research Experience for Undergraduates Award 1359026 and the Department of Energy, Laboratory Directed Research and Development Contract DE-AC05-06OR23177.
Initial NIST AC QHR Measurements
Cage, M. E.; Shields, S. H.; Jeffery, A.
2004-01-01
We demonstrate that dc quantized Hall resistance (dc QHR) guideline properties and dc and ac QHR values can be measured without changing sample probe lead connections at the QHR device, and report ac QHR values that converge to the dc QHR value when using four-terminal-pair ac QHR measurements. This was accomplished during one cooldown using single-series and quadruple-series connections outside the sample probe. The QHR was measured from 0 Hz to 5500 Hz in 1:1 ratio at 20 µA to ±1 part in 107 uncertainties with a poor-quality QHR device. A good device would allow an order of magnitude smaller uncertainties over this frequency range. We exchanged positions of the QHR device and reference resistor in the bridge and remeasured the resistance ratios to remove dominant ac bridge effects. PMID:27366620
Li, Jie-Ren; Lewandowski, Brian R; Xu, Song; Garno, Jayne C
2009-06-15
A new imaging strategy using atomic force microscopy (AFM) is demonstrated for mapping magnetic domains at size regimes below 100 nm. The AFM-based imaging mode is referred to as magnetic sample modulation (MSM), since the flux of an AC-generated electromagnetic field is used to induce physical movement of magnetic nanomaterials on surfaces during imaging. The AFM is operated in contact mode using a soft, nonmagnetic tip to detect the physical motion of the sample. By slowly scanning an AFM probe across a vibrating area of the sample, the frequency and amplitude of vibration induced by the magnetic field is tracked by changes in tip deflection. Thus, the AFM tip serves as a force and motion sensor for mapping the vibrational response of magnetic nanomaterials. Essentially, MSM is a hybrid of contact mode AFM combined with selective modulation of magnetic domains. The positional feedback loop for MSM imaging is the same as that used for force modulation and contact mode AFM; however, the vibration of the sample is analyzed using channels of a lock-in amplifier. The investigations are facilitated by nanofabrication methods combining particle lithography with organic vapor deposition and electroless deposition of iron oxide, to prepare designed test platforms of magnetic materials at nanometer length scales. Custom test platforms furnished suitable surfaces for MSM characterizations at the level of individual metal nanostructures.
A novel combined electrochemical-magnetic method for water treatment.
Ibanez, Jorge G; Vazquez-Olavarrieta, Jorge Luis; Hernandez-Rivera, Lydia; Garcia-Sanchez, Martin Adolfo; Garcia-Pintor, Elizabeth
2012-01-01
Electrocoagulation (EC) is a wastewater treatment process in which aqueous pollutants can be removed by adsorption, entrapment, precipitation or coalescence during a coagulation step produced by electrochemically generated metallic species. When using Fe as the sacrificial electrode, Fe(2+) and Fe(3+) ions are formed. As Fe(3+) species are paramagnetic, this property can in principle be used to facilitate their removal through the application of a magnetic field. In the present work we present a proof-of-concept for a combined electrochemical-magnetic method for pollutant removal. For this approach, the amounts of Fe(2+) and Fe(3+) produced in an EC cell at various voltages were measured by spectroscopic methods to confirm that Fe(3+) species predominate (up to 84%). The effectiveness of the presence of a magnetic field in the precipitation of coagulants from a suspension was confirmed by monitoring the turbidity change versus time with and without exposure to a magnetic field, up to a 30% improvement.
Chance-Constrained AC Optimal Power Flow for Distribution Systems With Renewables
DOE Office of Scientific and Technical Information (OSTI.GOV)
DallAnese, Emiliano; Baker, Kyri; Summers, Tyler
This paper focuses on distribution systems featuring renewable energy sources (RESs) and energy storage systems, and presents an AC optimal power flow (OPF) approach to optimize system-level performance objectives while coping with uncertainty in both RES generation and loads. The proposed method hinges on a chance-constrained AC OPF formulation where probabilistic constraints are utilized to enforce voltage regulation with prescribed probability. A computationally more affordable convex reformulation is developed by resorting to suitable linear approximations of the AC power-flow equations as well as convex approximations of the chance constraints. The approximate chance constraints provide conservative bounds that hold for arbitrarymore » distributions of the forecasting errors. An adaptive strategy is then obtained by embedding the proposed AC OPF task into a model predictive control framework. Finally, a distributed solver is developed to strategically distribute the solution of the optimization problems across utility and customers.« less
A Novel Method of Localization for Moving Objects with an Alternating Magnetic Field
Gao, Xiang; Yan, Shenggang; Li, Bin
2017-01-01
Magnetic detection technology has wide applications in the fields of geological exploration, biomedical treatment, wreck removal and localization of unexploded ordinance. A large number of methods have been developed to locate targets with static magnetic fields, however, the relation between the problem of localization of moving objectives with alternating magnetic fields and the localization with a static magnetic field is rarely studied. A novel method of target localization based on coherent demodulation was proposed in this paper. The problem of localization of moving objects with an alternating magnetic field was transformed into the localization with a static magnetic field. The Levenberg-Marquardt (L-M) algorithm was applied to calculate the position of the target with magnetic field data measured by a single three-component magnetic sensor. Theoretical simulation and experimental results demonstrate the effectiveness of the proposed method. PMID:28430153
Microstructure, hyperfine interaction and magnetic transition of Fe-25%Ni-5%Si-x%Co alloys
NASA Astrophysics Data System (ADS)
Gungunes, H.
2016-12-01
Morphological and magnetic properties in Fe-25%Ni-5%Si-x%Co (x = 0, 10, 15) alloys are investigated. Scanning electron microscopy (SEM), Mössbauer spectroscopy and AC magnetic susceptibility measurements are used to determine the physical properties of alloys. The martensite morphology changed depending on the Co content. The Mössbauer study shows that the volume fraction and hyperfine field of martensite increases while isomer shift values decrease with increasing Co content. On the other hand; AC susceptibility results showed that; Co is an effective element which can be used to control both the magnetic transition and martensitic transformation temperatures.
New perspectives on the dynamics of AC and DC plasma arcs exposed to cross-fields
NASA Astrophysics Data System (ADS)
Abdo, Youssef; Rohani, Vandad; Cauneau, François; Fulcheri, Laurent
2017-02-01
Interactions between an arc and external fields are crucially important for the design and the optimization of modern plasma torches. Multiple studies have been conducted to help better understand the behavior of DC and AC current arcs exposed to external and ‘self-induced’ magnetic fields, but the theoretical foundations remain very poorly explored. An analytical investigation has therefore been carried out in order to study the general behavior of DC and AC arcs under the effect of random cross-fields. A simple differential equation describing the general behavior of a planar DC or AC arc has been obtained. Several dimensionless numbers that depend primarily on arc and field parameters and the main arc characteristics (temperature, electric field strength) have also been determined. Their magnitude indicates the general tendency pattern of the arc evolution. The analytical results for many case studies have been validated using an MHD numerical model. The main purpose of this investigation was deriving a practical analytical model for the electric arc, rendering possible its stabilization and control, and the enhancement of the plasma torch power.
Spin ensemble-based AC magnetometry using concatenated dynamical decoupling at low temperatures
NASA Astrophysics Data System (ADS)
Farfurnik, D.; Jarmola, A.; Budker, D.; Bar-Gill, N.
2018-01-01
Ensembles of nitrogen-vacancy centers in diamond are widely used as AC magnetometers. While such measurements are usually performed using standard (XY) dynamical decoupling (DD) protocols at room temperature, we study the sensitivities achieved by utilizing various DD protocols, for measuring magnetic AC fields at frequencies in the 10-250 kHz range, at room temperature and 77 K. By performing measurements on an isotopically pure 12C sample, we find that the Carr-Purcell-Meiboom-Gill protocol, which is not robust against pulse imperfections, is less efficient for magnetometry than robust XY-based sequences. The concatenation of a standard XY-based protocol may enhance the sensitivities only for measuring high-frequency fields, for which many (> 500) DD pulses are necessary and the robustness against pulse imperfections is critical. Moreover, we show that cooling is effective only for measuring low-frequency fields (˜10 kHz), for which the experiment time approaches T 1 at a small number of applied DD pulses.
Rovina, Kobun; Siddiquee, Shafiquzzaman; Shaarani, Sharifudin M.
2016-01-01
Allura Red AC (E129) is an azo dye that widely used in drinks, juices, bakery, meat, and sweets products. High consumption of Allura Red has claimed an adverse effects of human health including allergies, food intolerance, cancer, multiple sclerosis, attention deficit hyperactivity disorder, brain damage, nausea, cardiac disease and asthma due to the reaction of aromatic azo compounds (R = R′ = aromatic). Several countries have banned and strictly controlled the uses of Allura Red in food and beverage products. This review paper is critically summarized on the available analytical and advanced methods for determination of Allura Red and also concisely discussed on the acceptable daily intake, toxicology and extraction methods. PMID:27303385
Chen, Shih-Wei; Lai, Jr-Jie; Chiang, Chen-Li; Chen, Cheng-Lung
2012-06-01
Magnetic hyperthermia using magnetic nanoparticles (MNPs) has attracted considerable attention as one of the promising tumor therapy. The study has been developed under single magnetic field. Recently, we found that the immobile MNP may generate more heat under two synchronous ac magnetic fields than traditional single and circular polarized fields based on model simulation result. According to this finding we constructed an orthogonal synchronized bi-directional field (OSB field). The system contained two LC resonant inverters (L: inductor, C: capacitor) and both vertical and transverse ac magnetic fields were generated by two Helmholtz coils. To reduce the interference, the axis directional of two coils were arranged orthogonally. The experiments showed that the heating ability of aggregated MNPs is greatly enhanced under this newly designed OSB field without increasing the strength of magnetic field. The OSB field system provides a promising way for future clinical hyperthermia.
NASA Astrophysics Data System (ADS)
Chen, Shih-Wei; Lai-Jie, Jr.; Chiang, Chen-Li; Chen, Cheng-Lung
2012-06-01
Magnetic hyperthermia using magnetic nanoparticles (MNPs) has attracted considerable attention as one of the promising tumor therapy. The study has been developed under single magnetic field. Recently, we found that the immobile MNP may generate more heat under two synchronous ac magnetic fields than traditional single and circular polarized fields based on model simulation result. According to this finding we constructed an orthogonal synchronized bi-directional field (OSB field). The system contained two LC resonant inverters (L: inductor, C: capacitor) and both vertical and transverse ac magnetic fields were generated by two Helmholtz coils. To reduce the interference, the axis directional of two coils were arranged orthogonally. The experiments showed that the heating ability of aggregated MNPs is greatly enhanced under this newly designed OSB field without increasing the strength of magnetic field. The OSB field system provides a promising way for future clinical hyperthermia.
A magnetic method for determining the geometry of hydraulic fractures
Byerlee, J.D.; Johnston, M.J.S.
1976-01-01
We propose a method that may be used to determine the spatial orientation of the fracture plane developed during hydraulic fracture. In the method, magnetic particles are injected into the crack with the fracturing fluid so as to generate a sheet of magnetized material. Since the magnetization of a body with extreme dimension ratios, such as a crack, exceeds that of an equidimensional body and since this magnetization is sensitive both to orientation and geometry, this could be used to obtain information about the crack. By measuring the vertical and horizontal components of the magnetic field and field gradients at the earth's surface surrounding the injection well with superconducting magnetometers having 10-4 gamma sensitivity and also by measuring field direction within the well itself, it should be possible to calculate the orientation and perhaps infer the approximate geometry of the fracture surface. Experiments on electric field potential operated in conjunction with this experiment could further constrain estimates of shape and orientation. ?? 1976 Birkha??user Verlag.
Single molecule magnet behaviour in robust dysprosium-biradical complexes.
Bernot, Kevin; Pointillart, Fabrice; Rosa, Patrick; Etienne, Mael; Sessoli, Roberta; Gatteschi, Dante
2010-09-21
A Dy-biradical complex was synthesized and characterized down to very low temperature. ac magnetic measurements reveal single molecule magnet behaviour visible without any application of dc field. The transition to the quantum tunneling regime is evidenced. Photophysical and EPR measurements provide evidence of the excellent stability of these complexes in solution.
AC Conductivity and Dielectric Properties of Borotellurite Glass
NASA Astrophysics Data System (ADS)
Taha, T. A.; Azab, A. A.
2016-10-01
Borotellurite glasses with formula 60B2O3-10ZnO-(30 - x)NaF- xTeO2 ( x = 0 mol.%, 5 mol.%, 10 mol.%, and 15 mol.%) have been synthesized by thermal melting. X-ray diffraction (XRD) analysis confirmed that the glasses were amorphous. The glass density ( ρ) was determined by the Archimedes method at room temperature. The density ( ρ) and molar volume ( V m) were found to increase with increasing TeO2 content. The direct-current (DC) conductivity was measured in the temperature range from 473 K to 623 K, in which the electrical activation energy of ionic conduction increased from 0.27 eV to 0.48 eV with increasing TeO2 content from 0 mol.% to 15 mol.%. The dielectric parameters and alternating-current (AC) conductivity ( σ ac) were investigated in the frequency range from 1 kHz to 1 MHz and temperature range from 300 K to 633 K. The AC conductivity and dielectric constant decreased with increasing TeO2 content from 0 mol.% to 15 mol.%.
1988-02-01
sponsors of ACs, e.g. their cost in terms of the time lost by senior managers because of their partici.nnts as assessors. Emhasises the need to address...American Psychologist. 37, 180-189. Reports use of the AC method to study the progress of a group of managers over a period of time . The study included...on 254 managers attending an AC, for changes in validities over time . Peer and assessor ratings, along with linear combinations, were found
Yan, Liang; Zhu, Bo; Jiao, Zongxia; Chen, Chin-Yin; Chen, I-Ming
2014-01-01
An orientation measurement method based on Hall-effect sensors is proposed for permanent magnet (PM) spherical actuators with three-dimensional (3D) magnet array. As there is no contact between the measurement system and the rotor, this method could effectively avoid friction torque and additional inertial moment existing in conventional approaches. Curved surface fitting method based on exponential approximation is proposed to formulate the magnetic field distribution in 3D space. The comparison with conventional modeling method shows that it helps to improve the model accuracy. The Hall-effect sensors are distributed around the rotor with PM poles to detect the flux density at different points, and thus the rotor orientation can be computed from the measured results and analytical models. Experiments have been conducted on the developed research prototype of the spherical actuator to validate the accuracy of the analytical equations relating the rotor orientation and the value of magnetic flux density. The experimental results show that the proposed method can measure the rotor orientation precisely, and the measurement accuracy could be improved by the novel 3D magnet array. The study result could be used for real-time motion control of PM spherical actuators. PMID:25342000
Yan, Liang; Zhu, Bo; Jiao, Zongxia; Chen, Chin-Yin; Chen, I-Ming
2014-10-24
An orientation measurement method based on Hall-effect sensors is proposed for permanent magnet (PM) spherical actuators with three-dimensional (3D) magnet array. As there is no contact between the measurement system and the rotor, this method could effectively avoid friction torque and additional inertial moment existing in conventional approaches. Curved surface fitting method based on exponential approximation is proposed to formulate the magnetic field distribution in 3D space. The comparison with conventional modeling method shows that it helps to improve the model accuracy. The Hall-effect sensors are distributed around the rotor with PM poles to detect the flux density at different points, and thus the rotor orientation can be computed from the measured results and analytical models. Experiments have been conducted on the developed research prototype of the spherical actuator to validate the accuracy of the analytical equations relating the rotor orientation and the value of magnetic flux density. The experimental results show that the proposed method can measure the rotor orientation precisely, and the measurement accuracy could be improved by the novel 3D magnet array. The study result could be used for real-time motion control of PM spherical actuators.
Santos, Guilherme de C.; Barros, Amanda L.; de Oliveira, Carlos A. F.; da Luz, Leonis L.; da Silva, Fausthon F.; Demets, Grégoire J.-F.; Alves Júnior, Severino
2017-01-01
New porous composites LnBDC@AC (AC = Activated carbon, Ln = Eu and Gd and BDC = 1,4-benzenedicaboxylate) and CB[6]@AC (CB[6] = Cucurbit[6]uril) were obtained using hydrothermal route. The LnBDC and CB[B] are located inside the pore of the carbon materials as was observed in SEM-EDS, XRPD and FT-IR analysis. Porosimetry analysis showed values typically between AC and LnBDC material, with pore size and surface area, respectively, 29,56 Å and 353.98 m2g-1 for LnBDC@AC and 35,53 Å and 353.98 m2g-1 for CB[6]@AC. Both materials showed good absorptive capacity of metil orange (MO) and methylene blue (MB) with selectivity as a function of pH. For acid pH, both materials present selectivity by MB and alkaline pH for MO, with notable performance for CB[6]@AC. Additionally, europium luminescence was used as structural probe to investigate the coordination environment of Eu3+ ions in the EuBDC@AC composite after adsorption experiment. PMID:28107440
Phase diagram of the chiral magnet Cr1 /3NbS2 in a magnetic field
NASA Astrophysics Data System (ADS)
Tsuruta, K.; Mito, M.; Deguchi, H.; Kishine, J.; Kousaka, Y.; Akimitsu, J.; Inoue, K.
2016-03-01
We construct the phase diagram of the chiral magnet Cr1 /3NbS2 in a dc magnetic field (Hdc) using ac magnetic susceptibility measurements. At Hdc=0 , the ac response at the transition from the helical magnetic (HM) state to the paramagnetic (PM) state consists of a giant third-order harmonic component (M3 ω) and a first-order harmonic component (M1 ω). By applying Hdc perpendicular to the c axis, the HM state is transformed to the chiral soliton lattice (CSL) state, which is a superlattice tuned by Hdc. The above giant M3 ω is markedly suppressed at small Hdc. The CSL state is found to consist of CSL-1, with dominant helical texture and a poor ferromagnetic array, and CSL-2, with a large ferromagnetic array. The transition between CSL-1 and the PM state causes a linear magnetic response, the dominant component of which is the in-phase M1 ω. With increasing temperature, CSL-2 is transformed into the forced ferromagnetic (FFM) state, and ultimately the PM state is reached. The transition between CSL-2 and the FFM state consists of a large M3 ω and large out-of-phase M1 ω as well as in-phase M1 ω. The transition between the FMM and PM states also yields a linear magnetic response, like the CSL-1-PM-state transition. Five typical magnetic dynamics in the transitions among the HM state, CSL-1, CSL-2, FFM state, and PM state were identified according to the equivalent dynamical motion equation of a nonlinear spring model.
Calculation of AC loss in two-layer superconducting cable with equal currents in the layers
NASA Astrophysics Data System (ADS)
Erdogan, Muzaffer
2016-12-01
A new method for calculating AC loss of two-layer SC power transmission cables using the commercial software Comsol Multiphysics, relying on the approach of the equal partition of current between the layers is proposed. Applying the method to calculate the AC-loss in a cable composed of two coaxial cylindrical SC tubes, the results are in good agreement with the analytical ones of duoblock model. Applying the method to calculate the AC-losses of a cable composed of a cylindrical copper former, surrounded by two coaxial cylindrical layers of superconducting tapes embedded in an insulating medium with tape-on-tape and tape-on-gap configurations are compared. A good agreement between the duoblock model and the numerical results for the tape-on-gap cable is observed.
21 CFR 886.1850 - AC-powered slitlamp biomicroscope.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false AC-powered slitlamp biomicroscope. 886.1850... (CONTINUED) MEDICAL DEVICES OPHTHALMIC DEVICES Diagnostic Devices § 886.1850 AC-powered slitlamp biomicroscope. (a) Identification. An AC-powered slitlamp biomicroscope is an AC-powered device that is a...
AC/DC current ratio in a current superimposition variable flux reluctance machine
NASA Astrophysics Data System (ADS)
Kohara, Akira; Hirata, Katsuhiro; Niguchi, Noboru; Takahara, Kazuaki
2018-05-01
We have proposed a current superimposition variable flux reluctance machine for traction motors. The torque-speed characteristics of this machine can be controlled by increasing or decreasing the DC current. In this paper, we discuss an AC/DC current ratio in the current superimposition variable flux reluctance machine. The structure and control method are described, and the characteristics are computed using FEA in several AC/DC ratios.
The equivalent magnetizing method applied to the design of gradient coils for MRI.
Lopez, Hector Sanchez; Liu, Feng; Crozier, Stuart
2008-01-01
This paper presents a new method for the design of gradient coils for Magnetic Resonance Imaging systems. The method is based on the equivalence between a magnetized volume surrounded by a conducting surface and its equivalent representation in surface current/charge density. We demonstrate that the curl of the vertical magnetization induces a surface current density whose stream line defines the coil current pattern. This method can be applied for coils wounds on arbitrary surface shapes. A single layer unshielded transverse gradient coil is designed and compared, with the designs obtained using two conventional methods. Through the presented example we demonstrate that the generated unconventional current patterns obtained using the magnetizing current method produces a superior gradient coil performance than coils designed by applying conventional methods.
A method of inversion of satellite magnetic anomaly data
NASA Technical Reports Server (NTRS)
Mayhew, M. A.
1977-01-01
A method of finding a first approximation to a crustal magnetization distribution from inversion of satellite magnetic anomaly data is described. Magnetization is expressed as a Fourier Series in a segment of spherical shell. Input to this procedure is an equivalent source representation of the observed anomaly field. Instability of the inversion occurs when high frequency noise is present in the input data, or when the series is carried to an excessively high wave number. Preliminary results are given for the United States and adjacent areas.
Magnetic Properties and Phase Diagram of Ni50Mn_{50-x}Ga_{x/2}In_{x/2} Magnetic Shape Memory Alloys
NASA Astrophysics Data System (ADS)
Xu, Xiao; Yoshida, Yasuki; Omori, Toshihiro; Kanomata, Takeshi; Kainuma, Ryosuke
2016-12-01
Ni50Mn50- x Ga x/2In x/2 magnetic shape memory alloys were systematically prepared, and the magnetic properties as well as the phase diagram, including atomic ordering, martensitic and magnetic transitions, were investigated. The B2- L21 order-disorder transformation showed a parabolic-like curve against the Ga+In composition. The martensitic transformation temperature was found to decrease with increasing Ga+In composition and to slightly bend downwards below the Curie temperature of the parent phase. Spontaneous magnetization was investigated for both parent and martensite alloys. The magnetism of martensite phase was found to show glassy magnetic behaviors by thermomagnetization and AC susceptibility measurements.
Analysis of the Distribution of Magnetic Fluid inside Tumors by a Giant Magnetoresistance Probe
Gooneratne, Chinthaka P.; Kurnicki, Adam; Yamada, Sotoshi; Mukhopadhyay, Subhas C.; Kosel, Jürgen
2013-01-01
Magnetic fluid hyperthermia (MFH) therapy uses the magnetic component of electromagnetic fields in the radiofrequency spectrum to couple energy to magnetic nanoparticles inside tumors. In MFH therapy, magnetic fluid is injected into tumors and an alternating current (AC) magnetic flux is applied to heat the magnetic fluid- filled tumor. If the temperature can be maintained at the therapeutic threshold of 42°C for 30 minutes or more, the tumor cells can be destroyed. Analyzing the distribution of the magnetic fluid injected into tumors prior to the heating step in MFH therapy is an essential criterion for homogenous heating of tumors, since a decision can then be taken on the strength and localization of the applied external AC magnetic flux density needed to destroy the tumor without affecting healthy cells. This paper proposes a methodology for analyzing the distribution of magnetic fluid in a tumor by a specifically designed giant magnetoresistance (GMR) probe prior to MFH heat treatment. Experimental results analyzing the distribution of magnetic fluid suggest that different magnetic fluid weight densities could be estimated inside a single tumor by the GMR probe. PMID:24312280
Lee, Won-Ho; Lee, Jong-Chul
2018-09-01
A numerical simulation was developed for magnetic nanoparticles in a liquid dielectric to investigate the AC breakdown voltage of the magnetic nanofluids according to the volume concentration of the magnetic nanoparticles. In prior research, we found that the dielectric breakdown voltage of the transformer oil-based magnetic nanofluids was positively or negatively affected according to the amount of magnetic nanoparticles under a testing condition of dielectric fluids, and the trajectory of the magnetic nanoparticles in a fabricated chip was visualized to verify the related phenomena via measurements and computations. In this study, a numerical simulation of magnetic nanoparticles in an insulating fluid was developed to model particle tracing for AC breakdown mechanisms happened to a sphere-sphere electrode configuration and to propose a possible mechanism regarding the change in the breakdown strength due to the behavior of the magnetic nanoparticles with different applied voltages.
Methods, systems and devices for detecting threatening objects and for classifying magnetic data
Kotter, Dale K [Shelley, ID; Roybal, Lyle G [Idaho Falls, ID; Rohrbaugh, David T [Idaho Falls, ID; Spencer, David F [Idaho Falls, ID
2012-01-24
A method for detecting threatening objects in a security screening system. The method includes a step of classifying unique features of magnetic data as representing a threatening object. Another step includes acquiring magnetic data. Another step includes determining if the acquired magnetic data comprises a unique feature.
Detection and characterisation of anthropogenic pieces by magnetic method
NASA Astrophysics Data System (ADS)
Nodot, Emilie; Munschy, Marc; Benevent, Pierre
2013-04-01
Human activities have let many anthropogenic objects buried under our feet. Some of these like explosive devices left after the World Wars turn out to be a threat to safety or environment. Others must be perfectly localised in case of construction work, for example gas pipe. Geophysics and more specifically magnetic cartography (many of these items are magnetic) can obviously help to locate them. We already use this method on daily basis to detect UXO (unexploded ordnance) but less than 10% of the unearthed objects are actually bombs or shells. Detection and mostly characterisation methods must be improved in order to reduce this proportion. On the field there are a few things we can do to increase data qualities. Characterisation may be improved by multiple scale prospections. We search a large area with our usual and rather fast method then we achieve high definition cartographies of small interesting areas (upon the object to characterise). In the case of measurements in an urban environment for example, data are distorted. The traffic (train, tramway, cars…) produces temporal variations of the magnetic field. This effect can be lessened, sometimes even removed by the use of a fixed scalar magnetic sensor. Data treatment is another key as regards the characterisation. Tools such as analytic signal or derivative are frequently used at the first degree. We will see that in a synthetic case the second and third degree bring even more information. A new issue appeared recently about pipes. Can we localise very precisely (less than 10 cm uncertainty) a gas pipe? Horizontally we can but due to our inversion method we still have troubles with the depth accuracy. Our final concern is about the amplitude of some anomalies. Potential methods equations are based on the fact that the anomaly norm must be minor to magnetic field norm. Sometimes this is not the case but vector magnetometry is a lead to solve this problem.
NASA Astrophysics Data System (ADS)
Hirano, R.; Kim, S. B.; Nakagawa, T.; Tomisaka, Y.; Ueda, H.
2017-07-01
The magnetic drug delivery system (MDDS) is a key technology to reduce the side effects in the medical applications, and the magnetic force control is very important issue in MDDS. In this application, the strength of magnetic field and gradient required to MDDS devices are 54 mT and 5.5 T/m, respectively. We proposed the new magnetic force control system that consists of the multiple racetrack HTS magnets. We can control the magnetic field gradient along the longitudinal direction by the arrangement of the multiple racetrack HTS magnets and operating current of each magnet. When the racetrack HTS magnets were used, the critical current was reduced by the self-magnetic field. Therefore, the shape design of HTS magnet to reduce the magnet field into the surface of HTS tapes was required. Therefore, the electromagnetic analysis based on finite element method (FEM) was carried out to design and optimize the shape of multiple racetrack HTS magnet. We were able to suppress the reduction of critical current by placing the magnetic substance at upper and lower side of the HTS magnets. It was confirmed that obtained maximum values of magnetic field strength and field gradient were 33 mT and 0.18 T/m, respectively.
NASA Astrophysics Data System (ADS)
Yamamoto, Y.; Ogasawara, J.; Himukai, H.; Itoh, T.
2016-10-01
In this paper, we report the heating properties of gold-magnetite (Au-Fe3O4) heterodimer nanoparticles (NPs) subjected to an alternating magnetic field. The Au-Fe3O4 NPs coated with oleic acid and oleylamine (OA) were synthesized through a method that combines seed mediation and high-temperature decomposition. The coating was replaced with dimercaptosuccinic acid (DMSA) by the ligand-exchange method. The specific absorption rates (SARs) for the OA- and DMSA-coated Au-Fe3O4 NPs coated with OA and DMSA at room temperature were determined through the calorimetric and magnetometric methods. SAR depended on the square of the magnetic field H up to an H value of 4 kA/m. The absolute value of the SAR for DMSA-coated NPs is about fivefold higher than that of the OA-coated NPs. The AC magnetic hysteresis measurements showed the recovery of the magnetic volume and the decrease in the magnetic anisotropy of the DMSA-coated NPs relative to those of the OA-coated NPs. These results suggest that the protective agent influences the magnetic properties of magnetite NPs via gold NPs.
Hayashi, Koichiro; Nakamura, Michihiro; Sakamoto, Wataru; Yogo, Toshinobu; Miki, Hirokazu; Ozaki, Shuji; Abe, Masahiro; Matsumoto, Toshio; Ishimura, Kazunori
2013-01-01
Superparamagnetic nanoparticles (SPIONs) could enable cancer theranostics if magnetic resonance imaging (MRI) and magnetic hyperthermia treatment (MHT) were combined. However, the particle size of SPIONs is smaller than the pores of fenestrated capillaries in normal tissues because superparamagnetism is expressed only at a particle size <10 nm. Therefore, SPIONs leak from the capillaries of normal tissues, resulting in low accumulation in tumors. Furthermore, MHT studies have been conducted in an impractical way: direct injection of magnetic materials into tumor and application of hazardous alternating current (AC) magnetic fields. To accomplish effective enhancement of MRI contrast agents in tumors and inhibition of tumor growth by MHT with intravenous injection and a safe AC magnetic field, we clustered SPIONs not only to prevent their leakage from fenestrated capillaries in normal tissues, but also for increasing their relaxivity and the specific absorption rate. We modified the clusters with folic acid (FA) and polyethylene glycol (PEG) to promote their accumulation in tumors. SPION clustering and cluster modification with FA and PEG were achieved simultaneously via the thiol-ene click reaction. Twenty-four hours after intravenous injection of FA- and PEG-modified SPION nanoclusters (FA-PEG-SPION NCs), they accumulated locally in cancer (not necrotic) tissues within the tumor and enhanced the MRI contrast. Furthermore, 24 h after intravenous injection of the NCs, the mice were placed in an AC magnetic field with H = 8 kA/m and f = 230 kHz (Hf = 1.8×10(9) A/m∙s) for 20 min. The tumors of the mice underwent local heating by application of an AC magnetic field. The temperature of the tumor was higher than the surrounding tissues by ≈6°C at 20 min after treatment. Thirty-five days after treatment, the tumor volume of treated mice was one-tenth that of the control mice. Furthermore, the treated mice were alive after 12 weeks; control mice died up to 8 weeks
Cantin, Luc; Deschenes, Mario; D'Amours, Mario
1995-08-15
A controller is provided for controlling operation of at least one electrical load operating on an AC supply having a typical frequency, the AC supply being provided via power transformers by an electrical power distribution grid. The controller is associated with the load and comprises an input interface for coupling the controller to the grid, a frequency detector for detecting the frequency of the AC supply and producing a signal indicative of the frequency, memory modules for storing preprogrammed commands, a frequency monitor for reading the signal indicative of the frequency and producing frequency data derived thereof, a selector for selecting at least one of the preprogrammed commands with respect to the frequency data, a control unit for producing at least one command signal representative of the selected preprogrammed commands, and an output interface including a device responsive to the command signal for controlling the load. Therefore, the load can be controlled by means of the controller depending on the frequency of the AC supply.
Apparatus and method for materials processing utilizing a rotating magnetic field
DOE Office of Scientific and Technical Information (OSTI.GOV)
Muralidharan, Govindarajan; Angelini, Joseph A.; Murphy, Bart L.
An apparatus for materials processing utilizing a rotating magnetic field comprises a platform for supporting a specimen, and a plurality of magnets underlying the platform. The plurality of magnets are configured for rotation about an axis of rotation intersecting the platform. A heat source is disposed above the platform for heating the specimen during the rotation of the plurality of magnets. A method for materials processing utilizing a rotating magnetic field comprises providing a specimen on a platform overlying a plurality of magnets; rotating the plurality of magnets about an axis of rotation intersecting the platform, thereby applying a rotatingmore » magnetic field to the specimen; and, while rotating the plurality of magnets, heating the specimen to a desired temperature.« less
Method for high resolution magnetic resonance analysis using magic angle technique
Wind, Robert A.; Hu, Jian Zhi
2003-12-30
A method of performing a magnetic resonance analysis of a biological object that includes placing the object in a main magnetic field (that has a static field direction) and in a radio frequency field; rotating the object at a frequency of less than about 100 Hz around an axis positioned at an angle of about 54.degree.44' relative to the main magnetic static field direction; pulsing the radio frequency to provide a sequence that includes a phase-corrected magic angle turning pulse segment; and collecting data generated by the pulsed radio frequency. The object may be reoriented about the magic angle axis between three predetermined positions that are related to each other by 120.degree.. The main magnetic field may be rotated mechanically or electronically. Methods for magnetic resonance imaging of the object are also described.
Method for high resolution magnetic resonance analysis using magic angle technique
Wind, Robert A.; Hu, Jian Zhi
2004-12-28
A method of performing a magnetic resonance analysis of a biological object that includes placing the object in a main magnetic field (that has a static field direction) and in a radio frequency field; rotating the object at a frequency of less than about 100 Hz around an axis positioned at an angle of about 54.degree.44' relative to the main magnetic static field direction; pulsing the radio frequency to provide a sequence that includes a phase-corrected magic angle turning pulse segment; and collecting data generated by the pulsed radio frequency. The object may be reoriented about the magic angle axis between three predetermined positions that are related to each other by 120.degree.. The main magnetic field may be rotated mechanically or electronically. Methods for magnetic resonance imaging of the object are also described.
High-Frequency ac Power-Distribution System
NASA Technical Reports Server (NTRS)
Hansen, Irving G.; Mildice, James
1987-01-01
Loads managed automatically under cycle-by-cycle control. 440-V rms, 20-kHz ac power system developed. System flexible, versatile, and "transparent" to user equipment, while maintaining high efficiency and low weight. Electrical source, from dc to 2,200-Hz ac converted to 440-V rms, 20-kHz, single-phase ac. Power distributed through low-inductance cables. Output power either dc or variable ac. Energy transferred per cycle reduced by factor of 50. Number of parts reduced by factor of about 5 and power loss reduced by two-thirds. Factors result in increased reliability and reduced costs. Used in any power-distribution system requiring high efficiency, high reliability, low weight, and flexibility to handle variety of sources and loads.
Method for making an improved magnetic encoding device
Fox, Richard J.
1981-01-01
A magnetic encoding device and method for making the same are provided for use as magnetic storage mediums in identification control applications which give output signals from a reader that are of shorter duration and substantially greater magnitude than those of the prior art. Magnetic encoding elements are produced by uniformly bending wire or strip stock of a magnetic material longitudinally about a common radius to exceed the elastic limit of the material and subsequently mounting the material so that it is restrained in an unbent position on a substrate of nonmagnetic material. The elements are spot weld attached to a substrate to form a binary coded array of elements according to a desired binary code. The coded substrate may be enclosed in a plastic laminate structure. Such devices may be used for security badges, key cards, and the like and may have many other applications.
NASA Technical Reports Server (NTRS)
Lawton, R. M.
1976-01-01
An analysis of magnetic fields in the Orbiter Payload Bay resulting from the present grounding configuration (structure return) was presented and the amount of improvement that would result from installing wire returns for the three dc power buses was determined. Ac and dc magnetic fields at five points in a cross-section of the bay are calculated for both grounding configurations. Y and Z components of the field at each point are derived in terms of a constant coefficient and the current amplitude of each bus. The dc loads assumed are 100 Amperes for each bus. The ac noise current used is a spectrum 6 db higher than the Orbiter equipment limit for narrowband conducted emissions. It was concluded that installing return wiring to provide a single point ground for the dc Buses in the Payload Bay would reduce the ac and dc magnetic field intensity by approximately 30 db.
78 FR 39345 - ACS Wireless, Inc.; Notice of Application
Federal Register 2010, 2011, 2012, 2013, 2014
2013-07-01
... on July 31, 1995 under the name MACTEL INC. Alaska Communications Systems Group, Inc. (``ACS Group...-owned subsidiary of ACS Group, held through ACS Group's wholly-owned subsidiary Alaska Communications... presently an investment company as defined in section 3(a) of the Act. 2. On June 4, 2012, ACS Group, ACS...
NASA Astrophysics Data System (ADS)
Richter, E.
1984-09-01
The work deals with the design and analysis study for the conceptual design of an economical high efficiency ac motor based on permanent magnets. The design and trade off studies have covered the material considerations, the design tradeoff options as well as transient and steady state performance considerations, and other options. The baseline comparison is the high efficiency induction motor. The permanent magnet (PM) motor must fit into the same frame size and surpass the induction motor on a life cost basis that includes 2.5 years of operation at a 50% duty cycle. It is shown that a motor based upon ferrite magnets does meet the objectives of the program in ratings of up to 25 hp. A 7.5 motor design is carried through the conceptual design stage.
Iterative optimization method for design of quantitative magnetization transfer imaging experiments.
Levesque, Ives R; Sled, John G; Pike, G Bruce
2011-09-01
Quantitative magnetization transfer imaging (QMTI) using spoiled gradient echo sequences with pulsed off-resonance saturation can be a time-consuming technique. A method is presented for selection of an optimum experimental design for quantitative magnetization transfer imaging based on the iterative reduction of a discrete sampling of the Z-spectrum. The applicability of the technique is demonstrated for human brain white matter imaging at 1.5 T and 3 T, and optimal designs are produced to target specific model parameters. The optimal number of measurements and the signal-to-noise ratio required for stable parameter estimation are also investigated. In vivo imaging results demonstrate that this optimal design approach substantially improves parameter map quality. The iterative method presented here provides an advantage over free form optimal design methods, in that pragmatic design constraints are readily incorporated. In particular, the presented method avoids clustering and repeated measures in the final experimental design, an attractive feature for the purpose of magnetization transfer model validation. The iterative optimal design technique is general and can be applied to any method of quantitative magnetization transfer imaging. Copyright © 2011 Wiley-Liss, Inc.
New Cogging Torque Reduction Methods for Permanent Magnet Machine
NASA Astrophysics Data System (ADS)
Bahrim, F. S.; Sulaiman, E.; Kumar, R.; Jusoh, L. I.
2017-08-01
Permanent magnet type motors (PMs) especially permanent magnet synchronous motor (PMSM) are expanding its limbs in industrial application system and widely used in various applications. The key features of this machine include high power and torque density, extending speed range, high efficiency, better dynamic performance and good flux-weakening capability. Nevertheless, high in cogging torque, which may cause noise and vibration, is one of the threat of the machine performance. Therefore, with the aid of 3-D finite element analysis (FEA) and simulation using JMAG Designer, this paper proposed new method for cogging torque reduction. Based on the simulation, methods of combining the skewing with radial pole pairing method and skewing with axial pole pairing method reduces the cogging torque effect up to 71.86% and 65.69% simultaneously.
Multiplex biosensing with highly sensitive magnetic nanoparticle quantification method
NASA Astrophysics Data System (ADS)
Nikitin, M. P.; Orlov, A. V.; Znoyko, S. L.; Bragina, V. A.; Gorshkov, B. G.; Ksenevich, T. I.; Cherkasov, V. R.; Nikitin, P. I.
2018-08-01
Unique properties of magnetic nanoparticles (MNP) have provided many breakthrough solutions for life science. The immense potential of MNP as labels in advanced immunoassays stems from the fact that they, unlike optical labels, can be easily detected inside 3D opaque porous biosensing structures or in colored mediums, manipulated by an external magnetic field, exhibit high stability and negligible background signal in biological samples, etc. In this research, the magnetic nanolabels and an original technique of their quantification by non-linear magnetization have permitted development of novel methods of multiplex biosensing. Several types of highly sensitive multi-channel readers that offer an extremely wide linear dynamic range are developed to count MNP in different recognition zones for quantitative concentration measurements of various analytes. Four approaches to multiplex biosensing based on MNP have been demonstrated in one-run tests based on several 3D porous structures; flat and micropillar microfluidic sensor chips; multi-line lateral flow strips and modular architecture of the strips, which is the first 3D multiplexing method that goes beyond the traditional planar techniques. Detection of cardio- and cancer markers, small molecules and oligonucleotides were used in the experiments. The analytical characteristics of the developed multiplex methods are on the level of the modern time-consuming laboratory techniques. The developed multiplex biosensing platforms are promising for medical and veterinary diagnostics, food inspection, environmental and security monitoring, etc.
In vitro and in vivo comparisons of constant resistance AC iontophoresis and DC iontophoresis.
Li, S Kevin; Higuchi, William I; Zhu, Honggang; Kern, Steven E; Miller, David J; Hastings, Matthew S
2003-09-04
A previous in vitro constant electrical resistance alternating current (AC) iontophoresis study with human epidermal membrane (HEM) and a model neutral permeant has shown less inter- and intra-sample variability in iontophoretic transport relative to conventional constant direct current (DC) iontophoresis. The objectives of the present study were to address the following questions. (1) Can the skin electrical resistance be maintained at a constant level by AC in humans in vivo? (2) Are the in vitro data with HEM representative of those in vivo? (3) Does constant skin resistance AC iontophoresis have less inter- and intra-sample variability than conventional constant current DC iontophoresis in vivo? (4) What are the electrical and the barrier properties of skin during iontophoresis in vivo? In the present study, in vitro HEM experiments were carried out with the constant resistance AC and the conventional constant current DC methods using mannitol and glucose as the neutral model permeants. In vivo human experiments were performed using glucose as the permeant with a constant skin resistance AC only protocol and two conventional constant current DC methods (continuous constant current DC and constant current DC with its polarity alternated every 10 min with a 3:7 on:off duty cycle). Constant current DC iontophoresis was conducted with commercial constant current DC devices, and constant resistance AC iontophoresis was carried out by reducing and maintaining the skin resistance at a constant target value with AC supplied from a function generator. This study shows that (1) skin electrical resistance can be maintained at a constant level during AC iontophoresis in vivo; (2) HEM in vitro and human skin in vivo demonstrate similar electrical and barrier properties, and these properties are consistent with our previous findings; (3) there is general qualitative and semi-quantitative agreement between the HEM data in vitro and human skin data in vivo; and (4) constant
A regularization method for extrapolation of solar potential magnetic fields
NASA Technical Reports Server (NTRS)
Gary, G. A.; Musielak, Z. E.
1992-01-01
The mathematical basis of a Tikhonov regularization method for extrapolating the chromospheric-coronal magnetic field using photospheric vector magnetograms is discussed. The basic techniques show that the Cauchy initial value problem can be formulated for potential magnetic fields. The potential field analysis considers a set of linear, elliptic partial differential equations. It is found that, by introducing an appropriate smoothing of the initial data of the Cauchy potential problem, an approximate Fourier integral solution is found, and an upper bound to the error in the solution is derived. This specific regularization technique, which is a function of magnetograph measurement sensitivities, provides a method to extrapolate the potential magnetic field above an active region into the chromosphere and low corona.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Yun, Hongseok; Kim, Jungkwun; Allen, Mark G.
2016-03-21
We investigate the ac magnetic behavior of solution processable, non-stoichiometric zinc ferrite nanocrystals with a series of sizes and zinc concentrations. Nearly monodisperse Zn{sub x}Fe{sub 3−x}O{sub 4} nanocrystals (x = 0–0.25) with an average size ranging from 7.4 nm to 13.8 nm are synthesized by using a solvothermal method. All the nanocrystals are in a superparamagnetic state at 300 K, which is confirmed by Superconductive Quantum Interference Device magnetometry. Due to the doping of non-magnetic Zn{sup 2+} into A site of ferrite, the saturation magnetization of nanocrystals increases as the size and Zn concentration increases. The ac magnetic permeability measurements at radio frequencies reveal thatmore » the real part of the magnetic permeability of similarly sized ferrite nanocrystals can be enhanced by almost twofold as the Zn{sup 2+} doping level increases from 0 to 0.25. The integration of 12.3 nm Zn{sub 0.25}Fe{sub 2.75}O{sub 4} nanocrystals into a toroidal inductor and a solenoid inductor prepared via a simple solution cast process yields a higher quality factors than air core inductors with the same geometries up to 5 MHz and 9 MHz, respectively, which is in the regime of the switching frequencies for the advanced integrated power converters.« less
Ring magnet firing angle control
Knott, M.J.; Lewis, L.G.; Rabe, H.H.
1975-10-21
A device is provided for controlling the firing angles of thyratrons (rectifiers) in a ring magnet power supply. A phase lock loop develops a smooth ac signal of frequency equal to and in phase with the frequency of the voltage wave developed by the main generator of the power supply. A counter that counts from zero to a particular number each cycle of the main generator voltage wave is synchronized with the smooth AC signal of the phase lock loop. Gates compare the number in the counter with predetermined desired firing angles for each thyratron and with coincidence the proper thyratron is fired at the predetermined firing angle.
NASA Technical Reports Server (NTRS)
Atwater, James; Wheeler, Richard, Jr.; Akse, James; Jovanovic, Goran; Reed, Brian
2013-01-01
To support long-duration manned missions in space such as a permanent lunar base, Mars transit, or Mars Surface Mission, improved methods for the treatment of solid wastes, particularly methods that recover valuable resources, are needed. The ability to operate under microgravity and hypogravity conditions is essential to meet this objective. The utilization of magnetic forces to manipulate granular magnetic media has provided the means to treat solid wastes under variable gravity conditions by filtration using a consolidated magnetic media bed followed by thermal processing of the solid wastes in a fluidized bed reactor. Non-uniform magnetic fields will produce a magnetic field gradient in a bed of magnetically susceptible media toward the distributor plate of a fluidized bed reactor. A correctly oriented magnetic field gradient will generate a downward direct force on magnetic media that can substitute for gravitational force in microgravity, or which may augment low levels of gravity, such as on the Moon or Mars. This approach is termed Gradient Magnetically Assisted Fluidization (G-MAFB), in which the magnitude of the force on the fluidized media depends upon the intensity of the magnetic field (H), the intensity of the field gradient (dH/dz), and the magnetic susceptibility of the media. Fluidized beds based on the G-MAFB process can operate in any gravitational environment by tuning the magnetic field appropriately. Magnetic materials and methods have been developed that enable G-MAFB operation under variable gravity conditions.
Donolato, Marco; Antunes, Paula; Bejhed, Rebecca S; Zardán Gómez de la Torre, Teresa; Østerberg, Frederik W; Strömberg, Mattias; Nilsson, Mats; Strømme, Maria; Svedlindh, Peter; Hansen, Mikkel F; Vavassori, Paolo
2015-02-03
We demonstrate detection of DNA coils formed from a Vibrio cholerae DNA target at picomolar concentrations using a novel optomagnetic approach exploiting the dynamic behavior and optical anisotropy of magnetic nanobead (MNB) assemblies. We establish that the complex second harmonic optical transmission spectra of MNB suspensions measured upon application of a weak uniaxial AC magnetic field correlate well with the rotation dynamics of the individual MNBs. Adding a target analyte to the solution leads to the formation of permanent MNB clusters, namely, to the suppression of the dynamic MNB behavior. We prove that the optical transmission spectra are highly sensitive to the formation of permanent MNB clusters and, thereby to the target analyte concentration. As a specific clinically relevant diagnostic case, we detect DNA coils formed via padlock probe recognition and isothermal rolling circle amplification and benchmark against a commercial equipment. The results demonstrate the fast optomagnetic readout of rolling circle products from bacterial DNA utilizing the dynamic properties of MNBs in a miniaturized and low-cost platform requiring only a transparent window in the chip.
Nonlinear magnetoelectric effects at high magnetic field amplitudes in composite multiferroics
NASA Astrophysics Data System (ADS)
Fetisov, L. Y.; Burdin, D. A.; Ekonomov, N. A.; Chashin, D. V.; Zhang, J.; Srinivasan, G.; Fetisov, Y. K.
2018-04-01
Magnetoelectric effects (ME) in ferromagnetic-ferroelectric layered composites arise due to magnetostriction and piezoelectric effect in the ferroic phases and are mediated by mechanical strain. The ME coupling strength in such composites could be measured by electrical response to an applied ac magnetic field h and a bias magnetic field H. The coupling, in general, is linear for small ac field amplitudes, but one expects nonlinear ME interactions for high field strengths since the dependence of magnetostriction λ on magnetic fields is nonlinear. Here we report on nonlinear voltage response of a composite of ferromagnetic Metglas and piezoelectric lanthanum gallium tantalate (langatate) subjected to an ac and a bias magnetic fields, resulting in the generation of voltages at harmonics of the frequency of h. The dependences of the ME voltage of the first four harmonics on the magnetic fields for H = 0–20 Oe and h = 0–50 Oe were measured. Up to a hundred harmonics were observed in the voltage versus frequency spectra and was indicative of high nonlinearity of the ME coupling in the multiferroic structure. It is shown that for h smaller than the saturation magnetic field H S for magnetostriction in the ferromagnetic layer, the amplitudes of the ME voltages are proportional to the derivatives of λ with respect to H and show a power-law dependence on the pumping field amplitude A n (H) ~ λ (n)(H)h n . We discuss a procedure for estimating the amplitudes of the harmonics for large pumping fields h, on the order of H S. The nonlinear ME effects in the composites are of interest for application in signal processing devices and highly sensitive magnetic field sensors.
NASA Astrophysics Data System (ADS)
Kuwahata, Akihiro; Kaneko, Miki; Chikaki, Shinichi; Kusakabe, Moriaki; Sekino, Masaki
2018-05-01
The developed device with electromagnetic coils and small permanent magnets quantifies the iron contents of superparamagnetic iron oxide nanoparticles for sentinel lymph node (SLN) biopsy. To remove diamagnetic and paramagnetic components and detect only superparamagnetic components, a 2nd harmonics signal is detected by a gradiometer under a moderate AC magnetic field (1-2 mT) with the fundamental frequency (2.944 kHz) of the coils and DC magnetic field (1-2 mT) of the magnets. The detection limit with a signal-to-noise ratio of 5 is approximately 0.28 μg of iron, and the device has a wide dynamic range of 104, 0.28 μg-2.8 mg. Additional coils and permanent magnets play an important role producing the optimum distribution of AC/DC magnetic fields for an iron distribution-independent and SLN size-independent quantification. We demonstrated the quantification of the iron in phantoms, which have a size of 3-20 mm with varied iron distributions and contain magnetic nanoparticles numerically. These results indicate that the developed device is useful for quantifying the magnetic nanoparticles accumulating in SLNs.
System and method of operating toroidal magnetic confinement devices
Chance, M.S.; Jardin, S.C.; Stix, T.H.; Grimm, R.C.; Manickam, J.; Okabayashi, M.
1984-08-30
This invention pertains to methods and arrangements for attaining high beta values in plasma confinement devices. More specifically, this invention pertains to methods for accessing the second stability region of operation in toroidal magnetic confinement devices.
AC conductivity and dielectric behavior of bulk Furfurylidenemalononitrile
NASA Astrophysics Data System (ADS)
El-Nahass, M. M.; Ali, H. A. M.
2012-06-01
AC conductivity and dielectric behavior for bulk Furfurylidenemalononitrile have been studied over a temperature range (293-333 K) and frequency range (50-5×106 Hz). The frequency dependence of ac conductivity, σac, has been investigated by the universal power law, σac(ω)=Aωs. The variation of the frequency exponent (s) with temperature was analyzed in terms of different conduction mechanisms, and it was found that the correlated barrier hopping (CBH) model is the predominant conduction mechanism. The temperature dependence of σac(ω) showed a linear increase with the increase in temperature at different frequencies. The ac activation energy was determined at different frequencies. Dielectric data were analyzed using complex permittivity and complex electric modulus for bulk Furfurylidenemalononitrile at various temperatures.
DOE Office of Scientific and Technical Information (OSTI.GOV)
Sasaki, M.; Hara, Y.; Inoue, M.
1997-02-01
Transverse magnetoresistance and Hall effect of the charge-density-wave (CDW) material {eta}-Mo{sub 4}O{sub 11} have been measured at 4.2 K (second CDW state) by dc and ac methods over the frequency range 50{endash}500 kHz in pulsed magnetic fields up to 40 T. These quantities are both reversible and frequency independent for a low-field sweep up to near 10 T (=H{sub c}), beyond which an appreciable frequency-dependent hysteresis effect appears. The Cole-Cole plots of the real versus imaginary parts of the magnetoresistance at high magnetic fields show a monodispersion. The magnetic-field dependence of the real part of the ac Hall resistivity showsmore » interesting behaviors, peaking near H{sub c}, followed by a decrease with H and a leveling off at high fields, while the imaginary components are very small and less frequency dependent. Using a multicarrier model consisting of the remaining and nested electron and hole bands, we have performed computer simulations for these dc and ac magnetotransport quantities, in satisfactory agreement with the observations. We have taken into account (1) the Zeeman effect for two types of the remaining hole and electron bands, (2) the CDW-gap narrowing of the nested electron and hole bands, (3) magnetic-field-induced CDW-to-normal phase transition in part of these nested bands, and (4) the magnetic-field-induced {open_quotes}CDW oscillation{close_quotes} around some mean position of the CDW condensates (or thermal excitation of the CDW phasons over a pinning potential), according to the existing CDW model. {copyright} {ital 1997} {ital The American Physical Society}« less
Pixel-based CTE Correction of ACS/WFC: Modifications To The ACS Calibration Pipeline (CALACS)
NASA Astrophysics Data System (ADS)
Smith, Linda J.; Anderson, J.; Armstrong, A.; Avila, R.; Bedin, L.; Chiaberge, M.; Davis, M.; Ferguson, B.; Fruchter, A.; Golimowski, D.; Grogin, N.; Hack, W.; Lim, P. L.; Lucas, R.; Maybhate, A.; McMaster, M.; Ogaz, S.; Suchkov, A.; Ubeda, L.
2012-01-01
The Advanced Camera for Surveys (ACS) was installed on the Hubble Space Telescope (HST) nearly ten years ago. Over the last decade, continuous exposure to the harsh radiation environment has degraded the charge transfer efficiency (CTE) of the CCDs. The worsening CTE impacts the science that can be obtained by altering the photometric, astrometric and morphological characteristics of sources, particularly those farthest from the readout amplifiers. To ameliorate these effects, Anderson & Bedin (2010, PASP, 122, 1035) developed a pixel-based empirical approach to correcting ACS data by characterizing the CTE profiles of trails behind warm pixels in dark exposures. The success of this technique means that it is now possible to correct full-frame ACS/WFC images for CTE degradation in the standard data calibration and reduction pipeline CALACS. Over the past year, the ACS team at STScI has developed, refined and tested the new software. The details of this work are described in separate posters. The new code is more effective at low flux levels (< 50 electrons) than the original Anderson & Bedin code, and employs a more accurate time and temperature dependence for CTE. The new CALACS includes the automatic removal of low-level bias stripes (produced by the post-repair ACS electronics) and pixel-based CTE correction. In addition to the standard cosmic ray corrected, flat-fielded and drizzled data products (crj, flt and drz files) there are three new equivalent files (crc, flc and drc) which contain the CTE-corrected data products. The user community will be able to choose whether to use the standard or CTE-corrected products.
Dynamic self-assembly and self-organized transport of magnetic micro-swimmers
DOE Office of Scientific and Technical Information (OSTI.GOV)
Kokot, Gasper; Kolmakov, German V.; Aranson, Igor S.
We demonstrate experimentally and in computer simulations that magnetic microfloaters can self-organize into various functional structures while energized by an external alternating (ac) magnetic field. The structures exhibit self-propelled motion and an ability to carry a cargo along a pre-defined path. As a result, the morphology of the self-assembled swimmers is controlled by the frequency and amplitude of the magnetic field.
Dynamic self-assembly and self-organized transport of magnetic micro-swimmers
Kokot, Gasper; Kolmakov, German V.; Aranson, Igor S.; ...
2017-11-07
We demonstrate experimentally and in computer simulations that magnetic microfloaters can self-organize into various functional structures while energized by an external alternating (ac) magnetic field. The structures exhibit self-propelled motion and an ability to carry a cargo along a pre-defined path. As a result, the morphology of the self-assembled swimmers is controlled by the frequency and amplitude of the magnetic field.
Sedimentary basins reconnaissance using the magnetic Tilt-Depth method
Salem, A.; Williams, S.; Samson, E.; Fairhead, D.; Ravat, D.; Blakely, R.J.
2010-01-01
We compute the depth to the top of magnetic basement using the Tilt-Depth method from the best available magnetic anomaly grids covering the continental USA and Australia. For the USA, the Tilt-Depth estimates were compared with sediment thicknesses based on drilling data and show a correlation of 0.86 between the datasets. If random data were used then the correlation value goes to virtually zero. There is little to no lateral offset of the depth of basinal features although there is a tendency for the Tilt-Depth results to be slightly shallower than the drill depths. We also applied the Tilt-Depth method to a local-scale, relatively high-resolution aeromagnetic survey over the Olympic Peninsula of Washington State. The Tilt-Depth method successfully identified a variety of important tectonic elements known from geological mapping. Of particular interest, the Tilt-Depth method illuminated deep (3km) contacts within the non-magnetic sedimentary core of the Olympic Mountains, where magnetic anomalies are subdued and low in amplitude. For Australia, the Tilt-Depth estimates also give a good correlation with known areas of shallow basement and sedimentary basins. Our estimates of basement depth are not restricted to regional analysis but work equally well at the micro scale (basin scale) with depth estimates agreeing well with drill hole and seismic data. We focus on the eastern Officer Basin as an example of basin scale studies and find a good level of agreement between previously-derived basin models. However, our study potentially reveals depocentres not previously mapped due to the sparse distribution of well data. This example thus shows the potential additional advantage of the method in geological interpretation. The success of this study suggests that the Tilt-Depth method is useful in estimating the depth to crystalline basement when appropriate quality aeromagnetic anomaly data are used (i.e. line spacing on the order of or less than the expected depth to
Fully alternating, triaxial electric or magnetic fields offer new routes to fluid vorticity
Martin, James E.; Solis, Kyle J.
2014-10-31
Noncontact methods of generating strong fluid vorticity are important to problems involving heat and mass transfer, fluid mixing, active wetting, and droplet transport. Furthermore, because zero or even negative shear viscosities can be induced, vorticity can greatly extend the control range of the smart fluids used in magnetorheological devices. In recent work we have shown that a particular class of ac/ac/dc triaxial fields (so-called symmetry-breaking rational fields) can create strong vorticity in magnetic particle suspensions and have presented a theory of the vorticity that is based on the symmetry of the 2-d Lissajous trajectories of the field and its converse.more » In this paper we demonstrate that there are three countably infinite sets of fully alternating ac/ac/ac triaxial fields whose frequencies form rational triads that have the symmetry required to drive fluid vorticity. The symmetry of the 3-d Lissajous trajectories of the field and its converse can be derived and from this the direction of the vorticity axis can be predicted, as can the dependence of the sign of the vorticity on the phase relations between the three field components. Experimental results are presented that validate the symmetry theory. These discoveries significantly broaden the class of triaxial fields that can be exploited to produce strong noncontact flow.« less
NASA Astrophysics Data System (ADS)
Yuan, Weijia; Coombs, T. A.; Kim, Jae-Ho; Han Kim, Chul; Kvitkovic, Jozef; Pamidi, Sastry
2011-12-01
Theoretical and experimental AC loss data on a superconducting pancake coil wound using second generation (2 G) conductors are presented. An anisotropic critical state model is used to calculate critical current and the AC losses of a superconducting pancake coil. In the coil there are two regions, the critical state region and the subcritical region. The model assumes that in the subcritical region the flux lines are parallel to the tape wide face. AC losses of the superconducting pancake coil are calculated using this model. Both calorimetric and electrical techniques were used to measure AC losses in the coil. The calorimetric method is based on measuring the boil-off rate of liquid nitrogen. The electric method used a compensation circuit to eliminate the inductive component to measure the loss voltage of the coil. The experimental results are consistent with the theoretical calculations thus validating the anisotropic critical state model for loss estimations in the superconducting pancake coil.
Poynting-vector based method for determining the bearing and location of electromagnetic sources
Simons, David J.; Carrigan, Charles R.; Harben, Philip E.; Kirkendall, Barry A.; Schultz, Craig A.
2008-10-21
A method and apparatus is utilized to determine the bearing and/or location of sources, such as, alternating current (A.C.) generators and loads, power lines, transformers and/or radio-frequency (RF) transmitters, emitting electromagnetic-wave energy for which a Poynting-Vector can be defined. When both a source and field sensors (electric and magnetic) are static, a bearing to the electromagnetic source can be obtained. If a single set of electric (E) and magnetic (B) sensors are in motion, multiple measurements permit location of the source. The method can be extended to networks of sensors allowing determination of the location of both stationary and moving sources.
van Ede, Freek
2017-01-01
Beta and gamma oscillations are the dominant oscillatory activity in the human motor cortex (M1). However, their physiological basis and precise functional significance remain poorly understood. Here, we used transcranial magnetic stimulation (TMS) to examine the physiological basis and behavioral relevance of driving beta and gamma oscillatory activity in the human M1 using transcranial alternating current stimulation (tACS). tACS was applied using a sham-controlled crossover design at individualized intensity for 20 min and TMS was performed at rest (before, during, and after tACS) and during movement preparation (before and after tACS). We demonstrated that driving gamma frequency oscillations using tACS led to a significant, duration-dependent decrease in local resting-state GABAA inhibition, as quantified by short interval intracortical inhibition. The magnitude of this effect was positively correlated with the magnitude of GABAA decrease during movement preparation, when gamma activity in motor circuitry is known to increase. In addition, gamma tACS-induced change in GABAA inhibition was closely related to performance in a motor learning task such that subjects who demonstrated a greater increase in GABAA inhibition also showed faster short-term learning. The findings presented here contribute to our understanding of the neurophysiological basis of motor rhythms and suggest that tACS may have similar physiological effects to endogenously driven local oscillatory activity. Moreover, the ability to modulate local interneuronal circuits by tACS in a behaviorally relevant manner provides a basis for tACS as a putative therapeutic intervention. SIGNIFICANCE STATEMENT Gamma oscillations have a vital role in motor control. Using a combined tACS-TMS approach, we demonstrate that driving gamma frequency oscillations modulates GABAA inhibition in the human motor cortex. Moreover, there is a clear relationship between the change in magnitude of GABAA inhibition induced
Nowak, Magdalena; Hinson, Emily; van Ede, Freek; Pogosyan, Alek; Guerra, Andrea; Quinn, Andrew; Brown, Peter; Stagg, Charlotte J
2017-04-26
Beta and gamma oscillations are the dominant oscillatory activity in the human motor cortex (M1). However, their physiological basis and precise functional significance remain poorly understood. Here, we used transcranial magnetic stimulation (TMS) to examine the physiological basis and behavioral relevance of driving beta and gamma oscillatory activity in the human M1 using transcranial alternating current stimulation (tACS). tACS was applied using a sham-controlled crossover design at individualized intensity for 20 min and TMS was performed at rest (before, during, and after tACS) and during movement preparation (before and after tACS). We demonstrated that driving gamma frequency oscillations using tACS led to a significant, duration-dependent decrease in local resting-state GABA A inhibition, as quantified by short interval intracortical inhibition. The magnitude of this effect was positively correlated with the magnitude of GABA A decrease during movement preparation, when gamma activity in motor circuitry is known to increase. In addition, gamma tACS-induced change in GABA A inhibition was closely related to performance in a motor learning task such that subjects who demonstrated a greater increase in GABA A inhibition also showed faster short-term learning. The findings presented here contribute to our understanding of the neurophysiological basis of motor rhythms and suggest that tACS may have similar physiological effects to endogenously driven local oscillatory activity. Moreover, the ability to modulate local interneuronal circuits by tACS in a behaviorally relevant manner provides a basis for tACS as a putative therapeutic intervention. SIGNIFICANCE STATEMENT Gamma oscillations have a vital role in motor control. Using a combined tACS-TMS approach, we demonstrate that driving gamma frequency oscillations modulates GABA A inhibition in the human motor cortex. Moreover, there is a clear relationship between the change in magnitude of GABA A inhibition
Magnetic characterization of isolated candidate vertebrate magnetoreceptor cells
Eder, Stephan H.K.; Cadiou, Hervé; Muhamad, Airina; McNaughton, Peter A.; Kirschvink, Joseph L.; Winklhofer, Michael
2012-01-01
Over the past 50 y, behavioral experiments have produced a large body of evidence for the existence of a magnetic sense in a wide range of animals. However, the underlying sensory physiology remains poorly understood due to the elusiveness of the magnetosensory structures. Here we present an effective method for isolating and characterizing potential magnetite-based magnetoreceptor cells. In essence, a rotating magnetic field is employed to visually identify, within a dissociated tissue preparation, cells that contain magnetic material by their rotational behavior. As a tissue of choice, we selected trout olfactory epithelium that has been previously suggested to host candidate magnetoreceptor cells. We were able to reproducibly detect magnetic cells and to determine their magnetic dipole moment. The obtained values (4 to 100 fAm2) greatly exceed previous estimates (0.5 fAm2). The magnetism of the cells is due to a μm-sized intracellular structure of iron-rich crystals, most likely single-domain magnetite. In confocal reflectance imaging, these produce bright reflective spots close to the cell membrane. The magnetic inclusions are found to be firmly coupled to the cell membrane, enabling a direct transduction of mechanical stress produced by magnetic torque acting on the cellular dipole in situ. Our results show that the magnetically identified cells clearly meet the physical requirements for a magnetoreceptor capable of rapidly detecting small changes in the external magnetic field. This would also explain interference of ac powerline magnetic fields with magnetoreception, as reported in cattle. PMID:22778440
Woolley, R.D.
1998-09-08
A method and apparatus are disclosed for the steady-state measurement of poloidal magnetic field near a tokamak plasma, where the tokamak is configured with respect to a cylindrical coordinate system having z, phi (toroidal), and r axes. The method is based on combining the two magnetic field principles of induction and torque. The apparatus includes a rotor assembly having a pair of inductive magnetic field pickup coils which are concentrically mounted, orthogonally oriented in the r and z directions, and coupled to remotely located electronics which include electronic integrators for determining magnetic field changes. The rotor assembly includes an axle oriented in the toroidal direction, with the axle mounted on pivot support brackets which in turn are mounted on a baseplate. First and second springs are located between the baseplate and the rotor assembly restricting rotation of the rotor assembly about its axle, the second spring providing a constant tensile preload in the first spring. A strain gauge is mounted on the first spring, and electronic means to continually monitor strain gauge resistance variations is provided. Electronic means for providing a known current pulse waveform to be periodically injected into each coil to create a time-varying torque on the rotor assembly in the toroidal direction causes mechanical strain variations proportional to the torque in the mounting means and springs so that strain gauge measurement of the variation provides periodic magnetic field measurements independent of the magnetic field measured by the electronic integrators. 6 figs.
Woolley, Robert D.
1998-01-01
A method and apparatus for the steady-state measurement of poloidal magnetic field near a tokamak plasma, where the tokamak is configured with respect to a cylindrical coordinate system having z, phi (toroidal), and r axes. The method is based on combining the two magnetic field principles of induction and torque. The apparatus includes a rotor assembly having a pair of inductive magnetic field pickup coils which are concentrically mounted, orthogonally oriented in the r and z directions, and coupled to remotely located electronics which include electronic integrators for determining magnetic field changes. The rotor assembly includes an axle oriented in the toroidal direction, with the axle mounted on pivot support brackets which in turn are mounted on a baseplate. First and second springs are located between the baseplate and the rotor assembly restricting rotation of the rotor assembly about its axle, the second spring providing a constant tensile preload in the first spring. A strain gauge is mounted on the first spring, and electronic means to continually monitor strain gauge resistance variations is provided. Electronic means for providing a known current pulse waveform to be periodically injected into each coil to create a time-varying torque on the rotor assembly in the toroidal direction causes mechanical strain variations proportional to the torque in the mounting means and springs so that strain gauge measurement of the variation provides periodic magnetic field measurements independent of the magnetic field measured by the electronic integrators.
Zaghi, Soroush; de Freitas Rezende, Larissa; de Oliveira, Laís Machado; El-Nazer, Rasheda; Menning, Sanne; Tadini, Laura; Fregni, Felipe
2010-08-02
There remains a lack of solid evidence showing whether transcranial stimulation with weak alternating current (transcranial alternating current stimulation, tACS) can in fact induce significant neurophysiological effects. Previously, a study in which tACS was applied for 2 and 5min with current density=0.16-0.25A/m(2) was unable to show robust effects on cortical excitability. Here we applied tACS at a significantly higher current density (0.80A/m(2)) for a considerably longer duration (20min) and were indeed able to demonstrate measurable changes to cortical excitability. Our results show that active 15Hz tACS of the motor cortex (electrodes placed at C3 and C4) significantly diminished the amplitude of motor evoked potentials and decreased intracortical facilitation (ICF) as compared to baseline and sham stimulation. In addition, we show that our method of sham tACS is a reliable control condition. These results support the notion that AC stimulation with weak currents can induce significant changes in brain excitability; in this case, 15Hz tACS led to a pattern of inhibition of cortical excitability. We propose that tACS may have a dampening effect on cortical networks and perhaps interfere with the temporal and spatial summation of weak subthreshold electric potentials. Copyright 2010 Elsevier Ireland Ltd. All rights reserved.
Robust, sensitive and facile method for detection of F-, CN- and Ac- anions
NASA Astrophysics Data System (ADS)
Madhusudhana Reddy, P.; Hsieh, Shih-Rong; Chen, Jem-Kun; Chang, Chi-Jung; Kang, Jing-Yuan; Chen, Chih-Hsien
2017-11-01
Sensing of F-, CN- and Ac- is important from the viewpoint of both medically and environmentally. Particularly, sensing of the anions in 100% water by a colorimetric chemical sensor is a highly difficult task as water molecules interfere the sensing mechanism. In this regard, sensor R1, having azo and nitrophenyl groups as signaling units and thiourea as a binding site was prepared. This sensor exclusively detected CN- ion over other testing anions in 30% aq. DMSO solution by exhibiting distinct spectral and visual color changes. However, in 15% aq. DMSO solution, R1 exhibited obvious spectral and color changes in response to F-, CN- and Ac-. On the other hand, we have also designed sensor, R2, having same signaling units of R1, but a different binding site of urea group. Surprisingly, in contrast to R1, R2 exhibited obvious spectral and color changes in 5% aq. DMSO solution only. Further, economically viable ;test stripes; were prepared in a facile mode to detect the CN- in 100% aqueous solution. Such stripes can serve as a practical colorimetric probe for ;in the field; detection of the ions and thus avoid additional expensive equipment.
NASA Astrophysics Data System (ADS)
Wen, Yan-Ni; Xia, Ming-Gang; Zhang, Sheng-Li
2016-05-01
By using the VASP, we studied the magnetic and electronic properties of the monolayer lateral hetero-junction WS2-MoS2-nanoribbons (WS2-MoS2-NRs). Our results show that the NRs' edge chirality and width affect significantly its magnetic and electronic properties. The monolayer lateral hetero-junction ZZ-WS2-MoS2-NRs(ZZ: zigzag) exhibitmetallic behavior and have considerable magnetic moment. Their magnetic moments decrease in the order of Nz = 2, 6 and 4 (the width of NRs). While, the magnetic moment decreases with the increased rz (the number of the Mo-S chains, rz ≠ 0 and rz ≠ Nz) at the same width Nz. The NA-AC-WS2-NR (AC: armchair) and NA-AC-WS2-MoS2-NR-1 (the number of the Mo-S chain is 1) show metallic behavior when NA = 3 (the width of NRs). The other monolayer lateral hetero-junction AC-WS2-MoS2-NRs remain the nonmagnetic and semiconductingbehavior as bulk. But they are indirect band-gap except for the NA = 3, rA = 2 (the number of the Mo-S chains) and NA = 7, rA = 0 when NA < 9. However they are direct band-gap when NA ≥ 9. Their lowest and highest band gaps are 0.150 eV and 0.581 eV, respectively. These unique magnetic and electronic properties will provide guidanceon the WS2-MoS2 hetero-junction application in nanodevice.
Ballweg, Verena; Eibofner, Frank; Graf, Hansjorg
2011-10-01
State of the art to access radiofrequency (RF) heating near implants is computer modeling of the devices and solving Maxwell's equations for the specific setup. For a set of input parameters, a fixed result is obtained. This work presents a theoretical approach in the alternating current (ac) limit, which can potentially render closed formulas for the basic behavior of tissue heating near metallic structures. Dedicated experiments were performed to support the theory. For the ac calculations, the implant was modeled as an RLC parallel circuit, with L being the secondary of a transformer and the RF transmission coil being its primary. Parameters influencing coupling, power matching, and specific absorption rate (SAR) were determined and formula relations were established. Experiments on a copper ring with a radial gap as capacitor for inductive coupling (at 1.5 T) and on needles for capacitive coupling (at 3 T) were carried out. The temperature rise in the embedding dielectric was observed as a function of its specific resistance using an infrared (IR) camera. Closed formulas containing the parameters of the setup were obtained for the frequency dependence of the transmitted power at fixed load resistance, for the calculation of the resistance for optimum power transfer, and for the calculation of the transmitted power in dependence of the load resistance. Good qualitative agreement was found between the course of the experimentally obtained heating curves and the theoretically determined power curves. Power matching revealed as critical parameter especially if the sample was resonant close to the Larmor frequency. The presented ac approach to RF heating near an implant, which mimics specific values for R, L, and C, allows for closed formulas to estimate the potential of RF energy transfer. A first reference point for worst-case determination in MR testing procedures can be obtained. Numerical approaches, necessary to determine spatially resolved heating maps, can
Magnetic nanorings and manipulation of nanowires
NASA Astrophysics Data System (ADS)
Chien, C. L.
2006-03-01
The properties of nanoscale entities, such as nanorings and nanowires, and the response of such entities to external fields are dictated by their geometrical shapes and sizes, which can be manipulated by fabrication. We have developed a method for fabricating a large number of nanorings (10^10) of different sizes in the range of 100 nm and ring cross sections. During magnetic reversal, both the vortex state and the rotating onion state appear with different proportions, which depend on the ring diameter, ring cross section, and the profile of the ring cross section. In the case of nanowires in suspension, the large aspect ratio of the nanowires can be exploited for manipulation despite extremely small Reynolds numbers of 10-5. Using AC electric field applied to microelectrodes, both magnetic and non-magnetic nanowires can be efficiently assembled into desired patterns. We also demonstrate rotation of nanowires with precisely controlled rotation speed and chirality, as well as an electrically driven nanowire micromotor a few in size. In collaboration with F. Q. Zhu, D. L. Fan, O. Tchernyshyov, R. C. Cammarata (Johns Hopkins University) and X. C. Zhu and J. G. Zhu (Carnegie-Mellon University).
Mishra, Om P; Popov, Anatoliy V; Pietrofesa, Ralph A; Christofidou-Solomidou, Melpo
2016-09-01
Secoisolariciresinol diglucoside (SDG), the main lignan in whole grain flaxseed, is a potent antioxidant and free radical scavenger with known radioprotective properties. However, the exact mechanism of SDG radioprotection is not well understood. The current study identified a novel mechanism of DNA radioprotection by SDG in physiological solutions by scavenging active chlorine species (ACS) and reducing chlorinated nucleobases. The ACS scavenging activity of SDG was determined using two highly specific fluoroprobes: hypochlorite-specific 3'-(p-aminophenyl) fluorescein (APF) and hydroxyl radical-sensitive 3'-(p-hydroxyphenyl) fluorescein (HPF). Dopamine, an SDG structural analog, was used for proton (1)H NMR studies to trap primary ACS radicals. Taurine N-chlorination was determined to demonstrate radiation-induced generation of hypochlorite, a secondary ACS. DNA protection was assessed by determining the extent of DNA fragmentation and plasmid DNA relaxation following exposure to ClO(-) and radiation. Purine base chlorination by ClO(-) and γ-radiation was determined by using 2-aminopurine (2-AP), a fluorescent analog of 6-aminopurine. Chloride anions (Cl(-)) consumed >90% of hydroxyl radicals in physiological solutions produced by γ-radiation resulting in ACS formation, which was detected by (1)H NMR. Importantly, SDG scavenged hypochlorite- and γ-radiation-induced ACS. In addition, SDG blunted ACS-induced fragmentation of calf thymus DNA and plasmid DNA relaxation. SDG treatment before or after ACS exposure decreased the ClO(-) or γ-radiation-induced chlorination of 2-AP. Exposure to γ-radiation resulted in increased taurine chlorination, indicative of ClO(-) generation. NMR studies revealed formation of primary ACS radicals (chlorine atoms (Cl) and dichloro radical anions (Cl2¯)), which were trapped by SDG and its structural analog dopamine. We demonstrate that γ-radiation induces the generation of ACS in physiological solutions. SDG treatment scavenged
Magnetic, hyperthermic and structural properties of zn substituted CaFe2O4 powders
NASA Astrophysics Data System (ADS)
Kheradmand, Abbas; Vahidi, Omid; Masoudpanah, S. M.
2018-03-01
In the present study, we have synthesized single phase Ca1 - x Zn x Fe2O4 powders by hydrothermal method. The cation distribution between the tetrahedral and octahedral sites in the spinel structure and the magnetic properties as a function of the zinc substitution have been investigated by X-ray diffraction (XRD), infrared spectroscopy and vibrating sample magnetometer methods. The obtained XRD pattern indicated that the synthesized particles had single phase cubic spinel structure with no impurity. The magnetic measurements showed that the saturation magnetization increased from 83 to 98 emu/g with the addition of zinc due to the decrease of inversity. The particle size observed by electron microscopy decreased from 1.38 to 0.97 µm with the increase of zinc addition. The Ca0.7Zn0.3Fe2O4 powders exhibited appropriate heating capability for hyperthermia applications with the maximum AC heating temperature of 20 °C and specific loss power of 9.29 W/g.
Superconductor coil geometry and ac losses
NASA Technical Reports Server (NTRS)
Pierce, T. V., Jr.; Zapata, R. N.
1976-01-01
An empirical relation is presented which allows simple computation of volume-averaged winding fields from central fields for coils of small rectangular cross sections. This relation suggests that, in certain applications, ac-loss minimization can be accomplished by use of low winding densities, provided that hysteresis losses are independent of winding density. The ac-loss measurements on coils wound of twisted multifilamentary composite superconductors show no significant dependence on ac losses on winding density, thus permitting the use of winding density as an independent design parameter in loss minimization.
A New Method for Coronal Magnetic Field Reconstruction
NASA Astrophysics Data System (ADS)
Yi, Sibaek; Choe, Gwang-Son; Cho, Kyung-Suk; Kim, Kap-Sung
2017-08-01
A precise way of coronal magnetic field reconstruction (extrapolation) is an indispensable tool for understanding of various solar activities. A variety of reconstruction codes have been developed so far and are available to researchers nowadays, but they more or less bear this and that shortcoming. In this paper, a new efficient method for coronal magnetic field reconstruction is presented. The method imposes only the normal components of magnetic field and current density at the bottom boundary to avoid the overspecification of the reconstruction problem, and employs vector potentials to guarantee the divergence-freeness. In our method, the normal component of current density is imposed, not by adjusting the tangential components of A, but by adjusting its normal component. This allows us to avoid a possible numerical instability that on and off arises in codes using A. In real reconstruction problems, the information for the lateral and top boundaries is absent. The arbitrariness of the boundary conditions imposed there as well as various preprocessing brings about the diversity of resulting solutions. We impose the source surface condition at the top boundary to accommodate flux imbalance, which always shows up in magnetograms. To enhance the convergence rate, we equip our code with a gradient-method type accelerator. Our code is tested on two analytical force-free solutions. When the solution is given only at the bottom boundary, our result surpasses competitors in most figures of merits devised by Schrijver et al. (2006). We have also applied our code to a real active region NOAA 11974, in which two M-class flares and a halo CME took place. The EUV observation shows a sudden appearance of an erupting loop before the first flare. Our numerical solutions show that two entwining flux tubes exist before the flare and their shackling is released after the CME with one of them opened up. We suggest that the erupting loop is created by magnetic reconnection between
Magnetoresistive DNA chips based on ac field focusing of magnetic labels
NASA Astrophysics Data System (ADS)
Ferreira, H. A.; Cardoso, F. A.; Ferreira, R.; Cardoso, S.; Freitas, P. P.
2006-04-01
A study was made on the sensitivity of a magnetoresistive DNA-chip platform being developed for cystic fibrosis diagnostics. The chip, comprised of an array of 2.5×80 μm2 U-shaped spin-valve sensors integrated within current line structures for magnetic label manipulation, enabled the detection at 30 Hz of 250 nm magnetic nanoparticles from 100 pM down to the pM range (or a target DNA concentration of 500 pM). It was observed that the sensor response increased linearly with label concentration. Noise spectra obtained for these sensors showed a thermal noise of 10-17 V2/Hz with a 1/f knee at 50 kHz at a 1 mA sense current, showing that lower detection limits are possible.
Martin, James E.; Solis, Kyle Jameson
2015-08-07
We recently reported two methods of inducing vigorous fluid vorticity in magnetic particle suspensions. The first method employs symmetry-breaking rational fields. These fields are comprised of two orthogonal ac components whose frequencies form a rational number and an orthogonal dc field that breaks the symmetry of the biaxial ac field to create the parity required to induce deterministic vorticity. The second method is based on rational triads, which are fields comprised of three orthogonal ac components whose frequency ratios are rational (e.g., 1 : 2 : 3). For each method a symmetry theory has been developed that enables the predictionmore » of the direction and sign of vorticity as functions of the field frequencies and phases. However, this theory has its limitations. It only applies to those particular phase angles that give rise to fields whose Lissajous plots, or principal 2-d projections thereof, have a high degree of symmetry. Nor can symmetry theory provide a measure of the magnitude of the torque density induced by the field. In this paper a functional of the multiaxial magnetic field is proposed that not only is consistent with all of the predictions of the symmetry theories, but also quantifies the torque density. This functional can be applied to fields whose Lissajous plots lack symmetry and can thus be used to predict a variety of effects and trends that cannot be predicted from the symmetry theories. These trends include the dependence of the magnitude of the torque density on the various frequency ratios, the unexpected reversal of flow with increasing dc field amplitude for certain symmetry-breaking fields, and the existence of off-axis vorticity for rational triads, such as 1 : 3 : 5, that do not have the symmetry required to analyze by symmetry theory. As a result, experimental data are given that show the degree to which this functional is successful in predicting observed trends.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)
Keating, Kristina; Slater, Lee; Ntarlagiannis, Dimitris
2015-02-24
This documents contains the final report for the project "Integrated Geophysical Measurements for Bioremediation Monitoring: Combining Spectral Induced Polarization, Nuclear Magnetic Resonance and Magnetic Methods" (DE-SC0007049) Executive Summary: Our research aimed to develop borehole measurement techniques capable of monitoring subsurface processes, such as changes in pore geometry and iron/sulfur geochemistry, associated with remediation of heavy metals and radionuclides. Previous work has demonstrated that geophysical method spectral induced polarization (SIP) can be used to assess subsurface contaminant remediation; however, SIP signals can be generated from multiple sources limiting their interpretation value. Integrating multiple geophysical methods, such as nuclear magnetic resonance (NMR)more » and magnetic susceptibility (MS), with SIP, could reduce the ambiguity of interpretation that might result from a single method. Our research efforts entails combining measurements from these methods, each sensitive to different mineral forms and/or mineral-fluid interfaces, providing better constraints on changes in subsurface biogeochemical processes and pore geometries significantly improving our understanding of processes impacting contaminant remediation. The Rifle Integrated Field Research Challenge (IFRC) site was used as a test location for our measurements. The Rifle IFRC site is located at a former uranium ore-processing facility in Rifle, Colorado. Leachate from spent mill tailings has resulted in residual uranium contamination of both groundwater and sediments within the local aquifer. Studies at the site include an ongoing acetate amendment strategy, native microbial populations are stimulated by introduction of carbon intended to alter redox conditions and immobilize uranium. To test the geophysical methods in the field, NMR and MS logging measurements were collected before, during, and after acetate amendment. Next, laboratory NMR, MS, and SIP
Slow magnetic relaxation at zero field in the tetrahedral complex [Co(SPh)4]2-.
Zadrozny, Joseph M; Long, Jeffrey R
2011-12-28
The Ph(4)P(+) salt of the tetrahedral complex [Co(SPh)(4)](2-), possessing an S = (3)/(2) ground state with an axial zero-field splitting of D = -70 cm(-1), displays single-molecule magnet behavior in the absence of an applied magnetic field. At very low temperatures, ac magnetic susceptibility data show the magnetic relaxation time, τ, to be temperature-independent, while above 2.5 K thermally activated Arrhenius behavior is apparent with U(eff) = 21(1) cm(-1) and τ(0) = 1.0(3) × 10(-7) s. Under an applied field of 1 kOe, τ more closely approximates Arrhenius behavior over the entire temperature range. Upon dilution of the complex within a matrix of the isomorphous compound (Ph(4)P)(2)[Zn(SPh)(4)], ac susceptibility data reveal the molecular nature of the slow magnetic relaxation and indicate that the quantum tunneling pathway observed at low temperatures is likely mediated by intermolecular dipolar interactions. © 2011 American Chemical Society
Methods for determining remanent and total magnetisations of magnetic sources - a review
NASA Astrophysics Data System (ADS)
Clark, David A.
2014-07-01
Assuming without evidence that magnetic sources are magnetised parallel to the geomagnetic field can seriously mislead interpretation and can result in drill holes missing their targets. This article reviews methods that are available for estimating, directly or indirectly, the natural remanent magnetisation (NRM) and total magnetisation of magnetic sources, noting the strengths and weaknesses of each approach. These methods are: (i) magnetic property measurements of samples; (ii) borehole magnetic measurements; (iii) inference of properties from petrographic/petrological information, supplemented by palaeomagnetic databases; (iv) constrained modelling/inversion of magnetic sources; (v) direct inversions of measured or calculated vector and gradient tensor data for simple sources; (vi) retrospective inference of magnetisation of a mined deposit by comparing magnetic data acquired pre- and post-mining; (vii) combined analysis of magnetic and gravity anomalies using Poisson's theorem; (viii) using a controlled magnetic source to probe the susceptibility distribution of the subsurface; (ix) Helbig-type analysis of gridded vector components, gradient tensor elements, and tensor invariants; (x) methods based on reduction to the pole and related transforms; and (xi) remote in situ determination of NRM direction, total magnetisation direction and Koenigsberger ratio by deploying dual vector magnetometers or a single combined gradiometer/magnetometer to monitor local perturbation of natural geomagnetic variations, operating in base station mode within a magnetic anomaly of interest. Characterising the total and remanent magnetisations of sources is important for several reasons. Knowledge of total magnetisation is often critical for accurate determination of source geometry and position. Knowledge of magnetic properties such as magnetisation intensity and Koenigsberger ratio constrains the likely magnetic mineralogy (composition and grain size) of a source, which gives an
Magnetization and transport properties of single RPd2P2 (R=Y, La-Nd, Sm-Ho, Yb)
NASA Astrophysics Data System (ADS)
Drachuck, Gil; Boehmer, Anna; Bud'Ko, Sergey L.; Canfield, Paul
Single crystals of RPd2P2 (R=Y, La-Nd, Sm-Ho, Yb) were grown using a self-flux method and were characterized by room-temperature powder X-ray diffraction, anisotropic temperature and field dependent magnetization and temperature dependent in-plane resistivity. Anisotropic magnetic properties, arising mostly from crystal electric field (CEF) effects, were observed for most magnetic rare earths. The experimentally estimated CEF parameters B02 were calculated from the anisotropic paramagnetic θab and θcvalues. Ordering temperatures, as well as the polycrystalline averaged paramagnetic Curie-Weiss temperature, θave, were extracted from magnetization and resistivity measurements. Work done at Ames Laboratory was supported by US Department of Energy, Basic Energy Sciences, Division of Materials Sciences and Engineering under Contract No. DE-AC02-07CH111358.
DC-biased AC-electroosmotic and AC-electrothermal flow mixing in microchannels.
Ng, Wee Yang; Goh, Shireen; Lam, Yee Cheong; Yang, Chun; Rodríguez, Isabel
2009-03-21
This paper presents a novel approach of mixing two laminar flowing streams in microchannels. The mixer consists of a pair of electrodes disposed along a fluidic channel. By energizing the electrodes with a DC-biased (2.5 V) AC voltage (20 Vpp), an electrokinetic flow is induced with a flow profile perpendicular to that of the incoming laminar streams of liquids to be mixed. As a result, the flow lines of the incoming streams and the induced flow are forced to crossover and very efficient stirring and mixing at short mixing length can be achieved. The mixer can be operated from the AC-electroosmotic (ACEO) (sigma=1 mS/m, f=100 kHz) to the AC-electrothermal (ACET) (sigma=500 mS/m, f=500 kHz) flow regimes. The mixing efficiency in the ACEO regime was 92%, with a mixing length of 600 microm (Q=2 microL/min), an estimated mixing time of 69 ms and an induced ACEO flow velocity of approximately 725 microm/s. The mixing efficiency in the ACET regime was 65% for a mixing length of approximately 1200 microm. The mixer is efficient and suitable for mixing reagents in a fluid media from low to high conductivity as required in diverse microfluidic applications.
Multiple magnetic transitions in EuNiSi3
NASA Astrophysics Data System (ADS)
Patil, Sujata M.; Paulose, P. L.
2018-04-01
EuNiSi3 undergoes multiple magnetic transitions below 50K. We have studied this system using low field ac susceptibility and 151Eu Mössbauer spectroscopy to understand the nature of multiple magnetic transitions. The estimated hyperfine field (hf) at Eu site at 5K is 45 Tesla which is unusually large compared to the normal observed hf of 33T in most of the Eu intermetallics.
Influence of martensitic transformation on the magnetic transition in Ni-Mn-Ga
NASA Astrophysics Data System (ADS)
Kokorin, V. V.; Konoplyuk, S. M.; Dalinger, A.; Maier, H. J.
2017-06-01
The magnetic transition with a temperature hysteresis of about 7 K was observed in the martensitic phase of Ni51.9Mn27Ga211. The measurements of AC magnetic susceptibility in constant magnetic fields up to 570 kA/m have proved its magnetic origin. The transport and caloric measurements were used to gain better understanding of the nature of this phenomenon. The variation of the martensite lattice parameters with temperature is suggested to account for the hysteresis of the magnetic transition.
Ion trajectory simulations of axial ac dipolar excitation in the Orbitrap
NASA Astrophysics Data System (ADS)
Wu, Guangxiang; Noll, Robert J.; Plass, Wolfgang R.; Hu, Qizhi; Perry, Richard H.; Cooks, R. Graham
2006-07-01
The newly developed version of the multi-particle ion trajectory simulation program, ITSIM 6.0, was applied to simulate ac dipolar excitation of ion axial motion in the Orbitrap. The Orbitrap inner and outer electrodes were generated in AutoCAD, a 3D drawing program. The electrode geometry was imported into the 3D field solver COMSOL; the field array was then imported into ITSIM 6.0. Ion trajectories were calculated by solving Newton's equations using Runge-Kutta integration methods. Compared to the analytical solution, calculated radial components of the field at the device's "equator" (z = 0) were within 0.5% and calculated axial components midway between the inner and outer electrodes were within 0.2%. The experiments simulated here involved the control of axial motion of ions in the Orbitrap by the application of dipolar ac signals to the split outer electrodes, as described in a recently published paper from this laboratory [Hu et al., J. Phys. Chem. A 110 (2006) 2682]. In these experiments, ac signal was applied at the axial resonant frequency of a selected ion. Axial excitation and eventual ion ejection resulted when the ac was in phase with, i.e., had 0° phase relative to ion axial motion. De-excitation of ion axial motion until the ions were at z = 0 and at rest with respect to the z-axis resulted if the applied ac was out of phase with ion motion, with re-excitation of ion axial motion occurring if the dipolar ac was continued beyond this point. Both de-excitation and re-excitation could be achieved mass-selectively and depended on the amplitude and duration (number of cycles) of the applied ac. The effects of ac amplitude, frequency, phase relative to ion motion, and bandwidth of applied waveform were simulated. All simulation results were compared directly with the experimental data and good agreement was observed. Such ion motion control experiments and their simulation provide the possibility to improve Orbitrap performance and to develop tandem mass
System and method for heating ferrite magnet motors for low temperatures
Reddy, Patel Bhageerath; El-Refaie, Ayman Mohamed Fawzi; Huh, Kum-Kang
2017-07-04
A system and method for heating ferrite permanent magnets in an electrical machine is disclosed. The permanent magnet machine includes a stator assembly and a rotor assembly, with a plurality of ferrite permanent magnets disposed within the stator assembly or the rotor assembly to generate a magnetic field that interacts with a stator magnetic field to produce a torque. A controller of the electrical machine is programmed to cause a primary field current to be applied to the stator windings to generate the stator magnetic field, so as to cause the rotor assembly to rotate relative to the stator assembly. The controller is further programmed to cause a secondary current to be applied to the stator windings to selectively generate a secondary magnetic field, the secondary magnetic field inducing eddy currents in at least one of the stator assembly and the rotor assembly to heat the ferrite permanent magnets.
Self-balanced modulation and magnetic rebalancing method for parallel multilevel inverters
DOE Office of Scientific and Technical Information (OSTI.GOV)
Li, Hui; Shi, Yanjun
A self-balanced modulation method and a closed-loop magnetic flux rebalancing control method for parallel multilevel inverters. The combination of the two methods provides for balancing of the magnetic flux of the inter-cell transformers (ICTs) of the parallel multilevel inverters without deteriorating the quality of the output voltage. In various embodiments a parallel multi-level inverter modulator is provide including a multi-channel comparator to generate a multiplexed digitized ideal waveform for a parallel multi-level inverter and a finite state machine (FSM) module coupled to the parallel multi-channel comparator, the FSM module to receive the multiplexed digitized ideal waveform and to generate amore » pulse width modulated gate-drive signal for each switching device of the parallel multi-level inverter. The system and method provides for optimization of the output voltage spectrum without influence the magnetic balancing.« less
ANALYSIS OF THE STRUCTURE OF MAGNETIC FIELDS THAT INDUCED INHIBITION OF STIMULATED NEURITE OUTGROWTH
The important experiments showing nonlinear amplitude dependences of the neurite outgrowth in pheochromocytoma nerve cells due to ELF magnetic field exposure had been carried out in a nonuniform ac magnetic field. The nonuniformity entailed larger than expected variances in magne...
AC and DC conductivity study on Ca substituted bismuth ferrite
NASA Astrophysics Data System (ADS)
Pandey, Rabichandra; Pradhan, Lagen Kumar; Kumar, Sunil; Kar, Manoranjan
2018-05-01
Bi0.95Ca0.05FeO3 multiferroic compound was synthesized by the citric acid modified sol-gel method. Crystal structure of Bi0.95Ca0.05FeO3 is studied by the X-ray diffraction (XRD) technique. The ac impedance analysis of the compound has been carried out in a wide range of frequency (100 Hz - 1MHz) as well as temperature (40-2500C). Frequency variation of dielectric constant at different temperatures can be understood by the modified Debye formula. The activation energy was found to be 0.48eV, which was obtained by employing Arrhenius equation. The AC conductivity of the sample follows the Johnscher's power law which indicates the presence of hopping type conduction in localized charged states. To understand the conduction mechanism with localized charge states, the DC resistivity data were analyzed by Mott's variable range hopping (VRH) model. The activation energy calculated from Debye relaxation time, AC conductivity and DC resistivity are comparable to each other.
The Hubble Legacy Archive ACS grism data
NASA Astrophysics Data System (ADS)
Kümmel, M.; Rosati, P.; Fosbury, R.; Haase, J.; Hook, R. N.; Kuntschner, H.; Lombardi, M.; Micol, A.; Nilsson, K. K.; Stoehr, F.; Walsh, J. R.
2011-06-01
A public release of slitless spectra, obtained with ACS/WFC and the G800L grism, is presented. Spectra were automatically extracted in a uniform way from 153 archival fields (or "associations") distributed across the two Galactic caps, covering all observations to 2008. The ACS G800L grism provides a wavelength range of 0.55-1.00 μm, with a dispersion of 40 Å/pixel and a resolution of ~80 Å for point-like sources. The ACS G800L images and matched direct images were reduced with an automatic pipeline that handles all steps from archive retrieval, alignment and astrometric calibration, direct image combination, catalogue generation, spectral extraction and collection of metadata. The large number of extracted spectra (73,581) demanded automatic methods for quality control and an automated classification algorithm was trained on the visual inspection of several thousand spectra. The final sample of quality controlled spectra includes 47 919 datasets (65% of the total number of extracted spectra) for 32 149 unique objects, with a median iAB-band magnitude of 23.7, reaching 26.5 AB for the faintest objects. Each released dataset contains science-ready 1D and 2D spectra, as well as multi-band image cutouts of corresponding sources and a useful preview page summarising the direct and slitless data, astrometric and photometric parameters. This release is part of the continuing effort to enhance the content of the Hubble Legacy Archive (HLA) with highly processed data products which significantly facilitate the scientific exploitation of the Hubble data. In order to characterize the slitless spectra, emission-line flux and equivalent width sensitivity of the ACS data were compared with public ground-based spectra in the GOODS-South field. An example list of emission line galaxies with two or more identified lines is also included, covering the redshift range 0.2 - 4.6. Almost all redshift determinations outside of the GOODS fields are new. The scope of science projects
Method of using triaxial magnetic fields for making particle structures
Martin, James E.; Anderson, Robert A.; Williamson, Rodney L.
2005-01-18
A method of producing three-dimensional particle structures with enhanced magnetic susceptibility in three dimensions by applying a triaxial energetic field to a magnetic particle suspension and subsequently stabilizing said particle structure. Combinations of direct current and alternating current fields in three dimensions produce particle gel structures, honeycomb structures, and foam-like structures.
Calibration of low-temperature ac susceptometers with a copper cylinder standard
DOE Office of Scientific and Technical Information (OSTI.GOV)
Chen, D.-X.; Skumryev, V.
2010-02-15
A high-quality low-temperature ac susceptometer is calibrated by comparing the measured ac susceptibility of a copper cylinder with its eddy-current ac susceptibility accurately calculated. Different from conventional calibration techniques that compare the measured results with the known property of a standard sample at certain fixed temperature T, field amplitude H{sub m}, and frequency f, to get a magnitude correction factor, here, the electromagnetic properties of the copper cylinder are unknown and are determined during the calibration of the ac susceptometer in the entire T, H{sub m}, and f range. It is shown that the maximum magnitude error and the maximummore » phase error of the susceptometer are less than 0.7% and 0.3 deg., respectively, in the region T=5-300 K and f=111-1111 Hz at H{sub m}=800 A/m, after a magnitude correction by a constant factor as done in a conventional calibration. However, the magnitude and phase errors can reach 2% and 4.3 deg. at 10 000 and 11 Hz, respectively. Since the errors are reproducible, a large portion of them may be further corrected after a calibration, the procedure for which is given. Conceptual discussions concerning the error sources, comparison with other calibration methods, and applications of ac susceptibility techniques are presented.« less
First results of transcritical magnetized collisionless shock studies on MSX
NASA Astrophysics Data System (ADS)
Weber, T. E.; Smith, R. J.; Hutchinson, T. M.; Taylor, S. F.; Hsu, S. C.
2014-10-01
Magnetized collisionless shocks exhibit transitional length and time scales much shorter than can be created through collisional processes. They are common throughout the cosmos, but have historically proven difficult to create in the laboratory. The Magnetized Shock Experiment (MSX) at LANL produces super-Alfvénic shocks through the acceleration and subsequent stagnation of Field Reversed Configuration (FRC) plasmoids against a strong magnetic mirror and flux-conserving vacuum boundary. Plasma flows have been produced with sonic and Alfvén Mach numbers up to ~10 over a wide range of plasma beta with embedded perpendicular, oblique, and parallel magnetic field. Macroscopic ion skin-depth and long ion-gyroperiod enable diagnostic access to relevant shock physics using common methods. Variable plasmoid velocity, density, temperature, and magnetic field provide access to a wide range of shock conditions, and a campaign to study the physics of transcritical and supercritical shocks within the FRC plasmoid is currently underway. An overview of the experimental design, diagnostics suite, physics objectives, and recent results will be presented. Supported by DOE Office of Fusion Energy Sciences under DOE Contract DE-AC52-06NA25369.
Measurement method of magnetic field for the wire suspended micro-pendulum accelerometer.
Lu, Yongle; Li, Leilei; Hu, Ning; Pan, Yingjun; Ren, Chunhua
2015-04-13
Force producer is one of the core components of a Wire Suspended Micro-Pendulum Accelerometer; and the stability of permanent magnet in the force producer determines the consistency of the acceleration sensor's scale factor. For an assembled accelerometer; direct measurement of magnetic field strength is not a feasible option; as the magnetometer probe cannot be laid inside the micro-space of the sensor. This paper proposed an indirect measurement method of the remnant magnetization of Micro-Pendulum Accelerometer. The measurement is based on the working principle of the accelerometer; using the current output at several different scenarios to resolve the remnant magnetization of the permanent magnet. Iterative Least Squares algorithm was used for the adjustment of the data due to nonlinearity of this problem. The calculated remnant magnetization was 1.035 T. Compared to the true value; the error was less than 0.001 T. The proposed method provides an effective theoretical guidance for measuring the magnetic field of the Wire Suspended Micro-Pendulum Accelerometer; correcting the scale factor and temperature influence coefficients; etc.
New functional materials AC3B4O12 (Review)
NASA Astrophysics Data System (ADS)
Vasil'ev, A. N.; Volkova, O. S.
2007-11-01
The physical properties of perovskites of the type AC3B4O12, whose structure derives from simple perovskites ABO3, are reviewed. The A position is subject to strong structural distortions and splits into two new positions A and C. In the structure of AC3B4O12 vacancies and any cations with a large radius, irrespective of their charge state, can be present in the icosahedral environment of A: Na +, Cd2+, Ca2+, Sr2+, Y3+, Ln3+, and Nd4+. The C position in the square environment of oxygen can be occupied only by the Jahn-Teller cations Cu2+ and Mn3+. Transition and nontransition metal ions—Mn3+, Fe3+, Al3+, Cr3+, Ti4+, Mn4+, Ge4+, Ru4+, Ir4+, Ta5+, Nb5+, Ta5+, Sb5+—can occupy the B position in an octahedral environment. Some members of the family of complex perovskites possess properties which are characteristic for systems with heavy fermions; collinear and noncollinear magnetic structures with high ordering temperatures occur in these materials; tunneling magnetoresistance and high permittivity are observed. The diversity and unique properties make these materials attractive for practical applications.
Stability mechanical considerations, and AC loss in HTSC monoliths, coils, and wires
NASA Technical Reports Server (NTRS)
Sumption, M. D.; Collings, E. W.
1995-01-01
For monolithic high-T(sub c) superconductors (HTSC's) calculations are presented of: (1) the initial flux jump field, H(sub fj), in melt-processed YBCO based on a field and temperature dependent J(sub c), and (2) the radial and circumferential stresses in solid and hollow cylinders containing trapped magnetic flux. For model multi filamentary (MF) HTSC/Ag strands calculations are presented of: (1) the limiting filament diameters for adiabatic and dynamic stability, and (2) the hysteretic and eddy current components of AC loss. Again for MF HTSC/Ag composite strands the need for filamentary subdivision and twisting is discussed.
Changes in stimulus and response AC/A ratio with vision therapy in Convergence Insufficiency.
Singh, Neeraj Kumar; Mani, Revathy; Hussaindeen, Jameel Rizwana
To evaluate the changes in the stimulus and response Accommodative Convergence to Accommodation (AC/A) ratio following vision therapy (VT) in Convergence Insufficiency (CI). Stimulus and response AC/A ratio were measured on twenty five CI participants, pre and post 10 sessions of VT. Stimulus AC/A ratio was measured using the gradient method and response AC/A ratio was calculated using modified Thorington technique with accommodative responses measured using WAM-5500 open-field autorefractor. The gradient stimulus and response AC/A cross-link ratios were compared with thirty age matched controls. Mean age of the CI and control participants were 23.3±5.2 years and 22.7±4.2 years, respectively. The mean stimulus and response AC/A ratio for CI pre therapy was 2.2±0.72 and 6.3±2.0 PD/D that changed to 4.2±0.9 and 8.28±3.31 PD/D respectively post vision therapy and these changes were statistically significant (paired t-test; p<0.001). The mean stimulus and response AC/A ratio for controls was 3.1±0.81 and 8.95±2.5 PD/D respectively. Stimulus and response AC/A ratio increased following VT, accompanied by clinically significant changes in vergence and accommodation parameters in subjects with convergence insufficiency. This represents the plasticity of the AC/A crosslink ratios that could be achieved with vision therapy in CI. Copyright © 2016 Spanish General Council of Optometry. Published by Elsevier España, S.L.U. All rights reserved.
Chen, Chen; Liu, Fei; Lin, Jun; Zhu, Kaiguang; Wang, Yanzhang
2016-04-12
The air-core coil sensor (ACS) is widely used as a transducer to measure the variation in magnetic fields of a helicopter transient electromagnetic (TEM) system. A high periodic emitting current induces the magnetic field signal of the underground medium. However, such current also generates a high primary field signal that can affect the received signal of the ACS and even damage the receiver. To increase the dynamic range of the received signal and to protect the receiver when emitting current rises/falls, the combination of ACS with magnetic flux compensation structure (bucking coil) is necessary. Moreover, the optimized ACS, which is composed of an air-core coil and a differential pre-amplifier circuit, must be investigated to meet the requirements of the helicopter TEM system suited to rapid surveying for shallow buried metal mine in rough topography. Accordingly, two ACSs are fabricated in this study, and their performance is verified and compared inside a magnetic shielding room. Using the designed ACSs, field experiments are conducted in Baoqing County. The field experimental data show that the primary field response can be compensated when the bucking coil is placed at an appropriate point in the range of allowed shift distance beyond the center of the transmitting coil and that the damage to the receiver induced by the over-statured signal can be solved. In conclusion, a more suitable ACS is adopted and is shown to have better performance, with a mass of 2.5 kg, resultant effective area of 11.6 m² (i.e., diameter of 0.496 m), 3 dB bandwidth of 66 kHz, signal-to-noise ratio of 4 (i.e., varying magnetic field strength of 0.2 nT/s), and normalized equivalent input noise of 3.62 nV/m².
A review of the magnetic properties, synthesis methods and applications of maghemite
NASA Astrophysics Data System (ADS)
Shokrollahi, H.
2017-03-01
It must be pointed out that maghemite (γ-Fe2O3) with a cubic spinel structure is a crucial material for various applications, including spin electronic devices, high-density magnetic recording, nano-medicines and biosensors. This paper has to do with a review study on the synthesis methods, magnetic properties and application of maghemite in the form of one-dimensional (1D) nanostructured materials, such as nanoparticles, nanotubes, nano-rods, and nanowires, as well as two-dimensional (2D) thin films. The results revealed that maghemite is widely used in the biomedical applications (hyperthermia, magnetic resonance imaging and drug delivery) and magnetic recording devices. The unmodified and Co/Mn modified maghemite thin films prepared by the dc-reactive magnetron sputtering show the excellent values of coercivity 2100 Oe and 3900 Oe, respectively, for the magnetic storage application. The super-paramagnetic particles with 7 nm size and the saturation magnetization of 80 emu/g prepared by the established thermolysis method are good candidates for bio-medical applications.
Advanced methods for controlling untethered magnetic devices using rotating magnetic fields
NASA Astrophysics Data System (ADS)
Mahoney, Arthur W., Jr.
This dissertation presents results documenting advancements on the control of untethered magnetic devices, such as magnetic "microrobots" and magnetically actuated capsule endoscopes, motivated by problems in minimally invasive medicine. This dissertation focuses on applying rotating magnetic fields for magnetic manipulation. The contributions include advancements in the way that helical microswimmers (devices that mimic the propulsion of bacterial flagella) are controlled in the presence of gravitational forces, advancements in ways that groups of untethered magnetic devices can be differentiated and semi-independently controlled, advancements in the way that untethered magnetic device can be controlled with a single rotating permanent magnet, and an improved understanding in the nature of the magnetic force applied to an untethered device by a rotating magnet.
NASA Astrophysics Data System (ADS)
Shibataki, Takuya; Takahashi, Yasuhito; Fujiwara, Koji
2018-04-01
This paper discusses a measurement method for saturation magnetizations of iron core materials using an electromagnet, which can apply an extremely large magnetic field strength to a specimen. It is said that electrical steel sheets are completely saturated at such a large magnetic field strength over about 100 kA/m. The saturation magnetization can be obtained by assuming that the completely saturated specimen shows a linear change of the flux density with the magnetic field strength because the saturation magnetization is constant. In order to accurately evaluate the flux density in the specimen, an air flux between the specimen and a winding of B-coil for detecting the flux density is compensated by utilizing an ideal condition that the incremental permeability of saturated specimen is equal to the permeability of vacuum. An error of magnetic field strength caused by setting a sensor does not affect the measurement accuracy of saturation magnetization. The error is conveniently cancelled because the saturation magnetization is a function of a ratio of the magnetic field strength to its increment. It may be concluded that the saturation magnetization can be easily measured with high accuracy by using the proposed method.
ACTIVITY ANALYSES FOR SOLAR-TYPE STARS OBSERVED WITH KEPLER. I. PROXIES OF MAGNETIC ACTIVITY
DOE Office of Scientific and Technical Information (OSTI.GOV)
He, Han; Wang, Huaning; Yun, Duo, E-mail: hehan@nao.cas.cn
2015-11-15
Light curves of solar-type stars often show gradual fluctuations due to rotational modulation by magnetic features (starspots and faculae) on stellar surfaces. Two quantitative measures of modulated light curves are employed as the proxies of magnetic activity for solar-type stars observed with Kepler telescope. The first is named autocorrelation index i{sub AC}, which describes the degree of periodicity of the light curve; the second is the effective fluctuation range of the light curve R{sub eff}, which reflects the depth of rotational modulation. The two measures are complementary and depict different aspects of magnetic activities on solar-type stars. By using themore » two proxies i{sub AC} and R{sub eff}, we analyzed activity properties of two carefully selected solar-type stars observed with Kepler (Kepler ID: 9766237 and 10864581), which have distinct rotational periods (14.7 versus 6.0 days). We also applied the two measures to the Sun for a comparative study. The result shows that both the measures can reveal cyclic activity variations (referred to as i{sub AC}-cycle and R{sub eff}-cycle) on the two Kepler stars and the Sun. For the Kepler star with the faster rotation rate, i{sub AC}-cycle and R{sub eff}-cycle are in the same phase, while for the Sun (slower rotator), they are in the opposite phase. By comparing the solar light curve with simultaneous photospheric magnetograms, it is identified that the magnetic feature that causes the periodic light curve during solar minima is the faculae of the enhanced network region, which can also be a candidate of magnetic features that dominate the periodic light curves on the two Kepler stars.« less
NASA Astrophysics Data System (ADS)
Anand, V. K.; Hillier, A. D.; Adroja, D. T.; Khalyavin, D. D.; Manuel, P.; Andre, G.; Rols, S.; Koza, M. M.
2018-05-01
The magnetic properties of a pressure induced noncentrosymmetric heavy-fermion superconductor CeIrGe3 have been investigated by muon spin relaxation (μ SR ), powder neutron diffraction (ND), and inelastic neutron scattering (INS) techniques at ambient pressure. For completeness we have also measured the ac magnetic susceptibility χac(T ) , dc magnetic susceptibility χ (T ) , dc isothermal magnetization M (H ) , and heat capacity Cp(T ,H ) down to 2 K. CeIrGe3 is known to exhibit pressure induced superconductivity (Tc≈1.5 K) at a pressure of 20 GPa and antiferromagnetic ordering at 8.7 K, 4.7 K, and 0.7 K at ambient pressure. Our χac(T ) and χ (T ) data show an additional anomaly near 6.2 K which is also captured in Cp(T ) data. From χac(T ) , χ (T ) , and Cp(T ) measurements we infer three antiferromagnetic transitions above 2 K at TN 1=8.5 K, TN 2=6.0 K, and TN 3=4.6 K. Our μ SR study also confirms the presence of three transitions through the observation of one frequency for TN 2
is shown that the maximum ac efficiency is equal to approximately 70% of the corresponding dc value. An illustrative example, including a proposed design for a rather unconventional transformer, is appended. (Author)
78 FR 49318 - Availability of Draft Advisory Circular (AC) 90-106A and AC 20-167A
Federal Register 2010, 2011, 2012, 2013, 2014
2013-08-13
... DEPARTMENT OF TRANSPORTATION Federal Aviation Administration [Docket No FAA-2013-0485] Availability of Draft Advisory Circular (AC) 90-106A and AC 20- 167A AGENCY: Federal Aviation Administration..., Federal Aviation Administration, 800 Independence Avenue SW., Washington, DC 20591; telephone (202) 385...
Input-current shaped ac to dc converters
NASA Technical Reports Server (NTRS)
1986-01-01
The problem of achieving near unity power factor while supplying power to a dc load from a single phase ac source of power is examined. Power processors for this application must perform three functions: input current shaping, energy storage, and output voltage regulation. The methods available for performing each of these three functions are reviewed. Input current shaping methods are either active or passive, with the active methods divided into buck-like and boost-like techniques. In addition to large reactances, energy storage methods include resonant filters, active filters, and active storage schemes. Fast voltage regulation can be achieved by post regulation or by supplementing the current shaping topology with an extra switch. Some indications of which methods are best suited for particular applications concludes the discussion.
Removal of algal blooms from freshwater by the coagulation-magnetic separation method.
Liu, Dan; Wang, Peng; Wei, Guanran; Dong, Wenbo; Hui, Franck
2013-01-01
This research investigated the feasibility of changing waste into useful materials for water treatment and proposed a coagulation-magnetic separation technique. This technique was rapid and highly effective for clearing up harmful algal blooms in freshwater and mitigating lake eutrophication. A magnetic coagulant was synthesized by compounding acid-modified fly ash with magnetite (Fe(3)O(4)). Its removal effects on algal cells and dissolved organics in water were studied. After mixing, coagulation, and magnetic separation, the flocs obtained from the magnet surface were examined by SEM. Treated samples were withdrawn for the content determination of chlorophyll-a, turbidity, chemical oxygen demand (COD), total nitrogen, and total phosphorus. More than 99 % of algal cells were removed within 5 min after the addition of magnetic coagulant at optimal loadings (200 mg L(-1)). The removal efficiencies of COD, total nitrogen, and phosphorus were 93, 91, and 94 %, respectively. The mechanism of algal removal explored preliminarily showed that the magnetic coagulant played multiple roles in mesoporous adsorption, netting and bridging, as well as high magnetic responsiveness to a magnetic field. The magnetic-coagulation separation method can rapidly and effectively remove algae from water bodies and greatly mitigate eutrophication of freshwater using a new magnetic coagulant. The method has good performance, is low cost, can turn waste into something valuable, and provides reference and directions for future pilot and production scale-ups.
Composite Materials with Magnetically Aligned Carbon Nanoparticles and Methods of Preparation
NASA Technical Reports Server (NTRS)
Salem, David R. (Inventor); Hong, Haiping (Inventor); Peterson, G.P. (Bud) (Inventor)
2018-01-01
The present invention relates to magnetically aligned carbon nanoparticle composites and methods of preparing the same. The composites comprise carbon nanoparticles, host material, magnetically sensitive nanoparticles and surfactant. The composites may have enhanced mechanical, thermal, and/or electrical properties.
Tuning the magnetism of ferrite nanoparticles
NASA Astrophysics Data System (ADS)
Viñas, S. Liébana; Simeonidis, K.; Li, Z.-A.; Ma, Z.; Myrovali, E.; Makridis, A.; Sakellari, D.; Angelakeris, M.; Wiedwald, U.; Spasova, M.; Farle, M.
2016-10-01
The importance of magnetic interactions within an individual nanoparticle or between adjacent ones is crucial not only for the macroscopic collective magnetic behavior but for the AC magnetic heating efficiency as well. On this concept, single-(MFe2O4 where M=Fe, Co, Mn) and core-shell ferrite nanoparticles consisting of a magnetically softer (MnFe2O4) or magnetically harder (CoFe2O4) core and a magnetite (Fe3O4) shell with an overall size in the 10 nm range were synthesized and studied for their magnetic particle hyperthermia efficiency. Magnetic measurements indicate that the coating of the hard magnetic phase (CoFe2O4) by Fe3O4 provides a significant enhancement of hysteresis losses over the corresponding single-phase counterpart response, and thus results in a multiplication of the magnetic hyperthermia efficiency opening a novel pathway for high-performance, magnetic hyperthermia agents. At the same time, the existence of a biocompatible Fe3O4 outer shell, toxicologically renders these systems similar to iron-oxide ones with significantly milder side-effects.
System and method for heating ferrite magnet motors for low temperatures
DOE Office of Scientific and Technical Information (OSTI.GOV)
Reddy, Patel Bhageerath; El-Refaie, Ayman Mohamed Fawzi; Huh, Kum-Kang
A system and method for heating ferrite permanent magnets in an electrical machine is disclosed. The permanent magnet machine includes a stator assembly and a rotor assembly, with a plurality of ferrite permanent magnets disposed within the stator assembly or the rotor assembly to generate a magnetic field that interacts with a stator magnetic field to produce a torque. A controller of the electrical machine is programmed to cause a primary field current to be applied to the stator windings to generate the stator magnetic field, so as to cause the rotor assembly to rotate relative to the stator assembly.more » The controller is further programmed to cause a secondary current to be applied to the stator windings to selectively generate a secondary magnetic field, the secondary magnetic field inducing eddy currents in at least one of the stator assembly and the rotor assembly to heat the ferrite permanent magnets.« less
McGary, John E; Xiong, Zubiao; Chen, Ji
2013-07-01
TomoTherapy systems lack real-time, tumor tracking. A possible solution is to use electromagnetic markers; however, eddy-current magnetic fields generated in response to a magnetic source can be comparable to the signal, thus degrading the localization accuracy. Therefore, the tracking system must be designed to account for the eddy fields created along the inner bore conducting surfaces. The aim of this work is to investigate localization accuracy using magnetic field gradients to determine feasibility toward TomoTherapy applications. Electromagnetic models are used to simulate magnetic fields created by a source and its simultaneous generation of eddy currents within a conducting cylinder. The source position is calculated using a least-squares fit of simulated sensor data using the dipole equation as the model equation. To account for field gradients across the sensor area (≈ 25 cm(2)), an iterative method is used to estimate the magnetic field at the sensor center. Spatial gradients are calculated with two arrays of uniaxial, paired sensors that form a gradiometer array, where the sensors are considered ideal. Experimental measurements of magnetic fields within the TomoTherapy bore are shown to be 1%-10% less than calculated with the electromagnetic model. Localization results using a 5 × 5 array of gradiometers are, in general, 2-4 times more accurate than a planar array of sensors, depending on the solenoid orientation and position. Simulation results show that the localization accuracy using a gradiometer array is within 1.3 mm over a distance of 20 cm from the array plane. In comparison, localization errors using single array are within 5 mm. The results indicate that the gradiometer method merits further studies and work due to the accuracy achieved with ideal sensors. Future studies should include realistic sensor models and extensive numerical studies to estimate the expected magnetic tracking accuracy within a TomoTherapy system before proceeding
NASA Astrophysics Data System (ADS)
Christodoulou, Dimitris M.; Contopoulos, John; Kazanas, Demosthenes
2003-03-01
We obtain the general forms of the axisymmetric stability criteria in a magnetized compressible Couette flow using an energy variational principle, the so-called interchange or Chandrasekhar's method, which we applied successfully in the incompressible case. This formulation accounts for the simultaneous presence of gravity, rotation, a toroidal magnetic field, a weak axial magnetic field, entropy gradients, and density gradients in the initial equilibrium state. The power of the method lies in its simplicity, which allows us to derive extremely compact and physically clear expressions for the relevant stability criteria despite the inclusion of so many physical effects. In the implementation of the method, all the applicable conservation laws are explicitly taken into account during the variations of a quantity with dimensions of energy that we call the ``free-energy function.'' As in the incompressible case, the presence of an axial field invalidates the conservation laws of angular momentum and azimuthal magnetic flux and introduces instead isorotation and axial current conservation along field lines. Our results are therefore markedly different depending on whether an axial magnetic field is present, and they generalize in two simple expressions all previously known, partial stability criteria for the appearance of magnetorotational instability. Furthermore, the coupling between magnetic tension and buoyancy and its influence to the dynamics of nonhomoentropic magnetized flows become quite clear from our results. In the limits of plane-parallel atmospheres and homoentropic flows, our formulation easily recovers the stability criteria for suppression of convective and Parker instabilities, as well as some related special cases studied over 40 years ago by Newcomb and Tserkovnikov via laborious variational techniques.
Vanitharani, Ramachandran; Chellappan, Padmanabhan; Pita, Justin S.; Fauquet, Claude M.
2004-01-01
Posttranscriptional gene silencing (PTGS) in plants is a natural defense mechanism against virus infection. In mixed infections, virus synergism is proposed to result from suppression of the host defense mechanism by the viruses. Synergistic severe mosaic disease caused by simultaneous infection with isolates of the Cameroon strain of African cassava mosaic virus (ACMV-[CM]) and East African cassava mosaic Cameroon virus (EACMCV) in cassava and tobacco is characterized by a dramatic increase in symptom severity and a severalfold increase in viral-DNA accumulation by both viruses compared to that in singly infected plants. Here, we report that synergism between ACMV-[CM] and EACMCV is a two-way process, as the presence of the DNA-A component of ACMV-[CM] or EACMCV in trans enhanced the accumulation of viral DNA of EACMCV and ACMV-[CM], respectively, in tobacco BY-2 protoplasts. Furthermore, transient expression of ACMV-[CM] AC4 driven by the Cauliflower mosaic virus 35S promoter (p35S-AC4) enhanced EACMCV DNA accumulation by ∼8-fold in protoplasts, while p35S-AC2 of EACMCV enhanced ACMV-[CM] DNA accumulation, also by ∼8-fold. An Agrobacterium-based leaf infiltration assay determined that ACMV-[CM] AC4 and EACMCV AC2, the putative synergistic genes, were able to suppress PTGS induced by green fluorescent protein (GFP) and eliminated the short interfering RNAs associated with PTGS, with a correlated increase in GFP mRNA accumulation. In addition, we have identified AC4 of Sri Lankan cassava mosaic virus and AC2 of Indian cassava mosaic virus as suppressors of PTGS, indicating that geminiviruses evolved differently in regard to interaction with the host. The specific and different roles played by these AC2 and AC4 proteins of cassava geminiviruses in regulating anti-PTGS activity and their relation to synergism are discussed. PMID:15308741
21 CFR 880.6320 - AC-powered medical examination light.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false AC-powered medical examination light. 880.6320... Miscellaneous Devices § 880.6320 AC-powered medical examination light. (a) Identification. An AC-powered medical examination light is an AC-powered device intended for medical purposes that is used to illuminate body...
Magnetic and transport properties of Pr2Pt3Si5
NASA Astrophysics Data System (ADS)
Anand, V. K.; Anupam; Hossain, Z.; Ramakrishnan, S.; Thamizhavel, A.; Adroja, D. T.
2012-08-01
We have investigated the magnetic and transport properties of a polycrystalline Pr2Pt3Si5 sample through the dc and ac magnetic susceptibilities, electrical resistivity, and specific heat measurements. The Rietveld refinement of the powder X-ray diffraction data reveals that Pr2Pt3Si5 crystallizes in the U2Co3Si5-type orthorhombic structure (space group Ibam). Both the dc and ac magnetic susceptibility data measured at low fields exhibit sharp anomaly near 15 K. In contrast, the specific heat data exhibit only a broad anomaly implying no long range magnetic order down to 2 K. The broad Schottky-type anomaly in low temperature specific heat data is interpreted in terms of crystal electric field (CEF) effect, and a CEF-split singlet ground state is inferred. The absence of the long range order is attributed to the presence of nonmagnetic singlet ground state of the Pr3+ ion. The electrical resistivity data exhibit metallic behavior and are well described by the Bloch-Grüniesen-Mott relation.
Magnetization-induced dynamics of a Josephson junction coupled to a nanomagnet
NASA Astrophysics Data System (ADS)
Ghosh, Roopayan; Maiti, Moitri; Shukrinov, Yury M.; Sengupta, K.
2017-11-01
We study the superconducting current of a Josephson junction (JJ) coupled to an external nanomagnet driven by a time-dependent magnetic field both without and in the presence of an external ac drive. We provide an analytic, albeit perturbative, solution for the Landau-Lifshitz (LL) equations governing the coupled JJ-nanomagnet system in the presence of a magnetic field with arbitrary time dependence oriented along the easy axis of the nanomagnet's magnetization and in the limit of weak dimensionless coupling ɛ0 between the JJ and the nanomagnet. We show the existence of Shapiro-type steps in the I -V characteristics of the JJ subjected to a voltage bias for a constant or periodically varying magnetic field and explore the effect of rotation of the magnetic field and the presence of an external ac drive on these steps. We support our analytic results with exact numerical solution of the LL equations. We also extend our results to dissipative nanomagnets by providing a perturbative solution to the Landau-Lifshitz-Gilbert (LLG) equations for weak dissipation. We study the fate of magnetization-induced Shapiro steps in the presence of dissipation both from our analytical results and via numerical solution of the coupled LLG equations. We discuss experiments which can test our theory.
Field-dependence of AC susceptibility in titanomagnetites
Jackson, M.; Moskowitz, B.; Rosenbaum, J.; Kissel, Catherie
1998-01-01
AC susceptibility measurements as a function of field amplitude Hac and of frequency show a strong field dependence for a set of synthetic titanomagnetites (Fe3-xTixO4) and for certain basalts from the SOH-1 Hawaiian drill hole and from Iceland. In-phase susceptibility is constant below fields of about 10-100 A/m, and then increases by as much as a factor of two as Hsc is increased to 2000 A/m. Both the initial field-independent susceptibilities and field-dependence of susceptibility are systematically related to composition: initial susceptibility is 3 SI for a single-crystal sphere of TMO (x = 0) and decreases with increasing titanium content; field-dependence is nearly zero for TM0 and increases systematically to a maximum near TM60 (x = 0.6). This field dependence can in some cases be mistaken for frequency dependence, and leaf to incorrect interpretations of magnetic grain size and composition when titanomagnetite is present.
NASA Astrophysics Data System (ADS)
Nakamura, D.; Altarawneh, M. M.; Takeyama, S.
2018-03-01
A contactless measurement system of electrical conductivity was developed for application under pulsed high magnetic fields over 100 T by using a self-resonant-type, high-frequency circuit. Electromagnetic fields in the circuit were numerically analysed by the finite element method, to show how the resonant power spectra of the circuit depends on the electrical conductivity of a sample set on the probe-coil. The performance was examined using a high-temperature cuprate superconductor, La2-x Sr x CuO4, in magnetic fields up to 102 T with a high frequency of close to 800 MHz. As a result, the upper critical field could be determined with a good signal-to-noise ratio.
High-frequency ac power distribution in Space Station
NASA Technical Reports Server (NTRS)
Tsai, Fu-Sheng; Lee, Fred C. Y.
1990-01-01
A utility-type 20-kHz ac power distribution system for the Space Station, employing resonant power-conversion techniques, is presented. The system converts raw dc voltage from photovoltaic cells or three-phase LF ac voltage from a solar dynamic generator into a regulated 20-kHz ac voltage for distribution among various loads. The results of EASY5 computer simulations of the local and global performance show that the system has fast response and good transient behavior. The ac bus voltage is effectively regulated using the phase-control scheme, which is demonstrated with both line and load variations. The feasibility of paralleling the driver-module outputs is illustrated with the driver modules synchronized and sharing a common feedback loop. An HF sinusoidal ac voltage is generated in the three-phase ac input case, when the driver modules are phased 120 deg away from one another and their outputs are connected in series.
Effects of DC bias on magnetic performance of high grades grain-oriented silicon steels
NASA Astrophysics Data System (ADS)
Ma, Guang; Cheng, Ling; Lu, Licheng; Yang, Fuyao; Chen, Xin; Zhu, Chengzhi
2017-03-01
When high voltage direct current (HVDC) transmission adopting mono-polar ground return operation mode or unbalanced bipolar operation mode, the invasion of DC current into neutral point of alternating current (AC) transformer will cause core saturation, temperature increasing, and vibration acceleration. Based on the MPG-200D soft magnetic measurement system, the influence of DC bias on magnetic performance of 0.23 mm and 0.27 mm series (P1.7=0.70-1.05 W/kg, B8>1.89 T) grain-oriented (GO) silicon steels under condition of AC / DC hybrid excitation were systematically realized in this paper. For the high magnetic induction GO steels (core losses are the same), greater thickness can lead to stronger ability of resisting DC bias, and the reasons for it were analyzed. Finally, the magnetostriction and A-weighted magnetostriction velocity level of GO steel under DC biased magnetization were researched.
The Response AC/A Ratio Before and After the Onset of Myopia
Mutti, Donald O.; Mitchell, G. Lynn; Jones-Jordan, Lisa A.; Cotter, Susan A.; Kleinstein, Robert N.; Manny, Ruth E.; Twelker, J. Daniel; Zadnik, Karla
2017-01-01
Purpose To investigate the ratio of accommodative convergence per diopter of accommodative response (AC/A ratio) before, during, and after myopia onset. Methods Subjects were 698 children aged 6 to 14 years who became myopic and 430 emmetropic children participating in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error. Refractive error was measured using cycloplegic autorefraction, near work by parent survey, and the AC/A ratio by simultaneously monitoring convergence and accommodative response. The response AC/A ratios of children who became myopic were compared with age-, sex-, and ethnicity-matched model estimates for emmetropic children from 5 years before through 5 years after the onset of myopia. Results The response AC/A ratio was not significantly different between the two groups 5 years before onset, then increased monotonically in children who became myopic until reaching a plateau at myopia onset of about 7 Δ/D compared to about 4 Δ/D for children who remained emmetropic (differences between groups significant at P < 0.01 from 4 years before onset through 5 years after onset). A higher AC/A ratio was associated with greater accommodative lag but not with the rate of myopia progression regardless of the level of near work. Conclusions An increasing AC/A ratio is an early sign of becoming myopic, is related to greater accommodative lag, but does not affect the rate of myopia progression. The association with accommodative lag suggests that the AC/A ratio increase is from greater neural effort needed per diopter of accommodation rather than change in the accommodative convergence crosslink gain relationship. PMID:28291868
NASA Astrophysics Data System (ADS)
Anjana, V.; John, Sara; Prakash, Pooja; Nair, Amritha M.; Nair, Aravind R.; Sambhudevan, Sreedha; Shankar, Balakrishnan
2018-02-01
Nickel ferrite nanoparticles with copper atoms as dopant have been prepared using co-precipitation method with general formula Ni1-xCuxFe2O4 (x=0.2, 0.4, 0.6, 0.8 and 1) and are sintered at quite ambient temperature. Structural and magnetic properties were examined using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction method (XRD) and Vibrating Sample Magnetometer (VSM) to study the influence of copper doping in nickel ferrite magnetic nanoparticles. X-ray studies proves that the particles are possessing single phase spinel structure with an average particle size calculated using Debye Scherer formula. Magnetic measurements reveal that saturation magnetization value (Ms) decreases while magnetic coercivity (Hc) increases upon doping.
NASA Astrophysics Data System (ADS)
Jiang, Zhao-Fei; Xue, Feng; Gou, Xiao-Fan
2018-04-01
The microstructure of Bi2Sr2CaCu2Ox (Bi2212) filamentary composite round wires (RWs) changes to be extremely complicated after heat treatment, with the interface between Bi2212 filaments and Ag matrix being meandering and a lot of bridge connections (BCs) generating between filaments. The influence of such the unique microstructure on the electromagnetic behavior and especially the AC loss has not been far from completely understanding. In this paper, according to the H formulation and on the nonlinear E-J relationship, we developed a finite element model, and further on this model evaluated the current and AC loss of a Bi2212 multifilamentary wire with the rough Bi2212/Ag interface and several BCs between filaments under the alternating magnetic field (Hex(t) = H0sin2πft). Through the comparative study, we found that the penetration magnetic field Hp is a critical turning point and on this base the influences of such the complex microstructure are quite different when the amplitude of applied magnetic field H0 < Hp and when H0 > Hp. The rough interface impacts the current distribution and causes the local heat concentrated at the concave locations. For BCs between Bi2212 filaments, it is most significant that they can share the current and make the current redistribute between filaments. Further for the wire with various types of BCs, the current distribution and the AC loss relative to the wire without BCs (Q / QmagnoBCs) were comprehensively investigated.
Thermoseeds for interstitial magnetic hyperthermia: from bioceramics to nanoparticles
NASA Astrophysics Data System (ADS)
Baeza, A.; Arcos, D.; Vallet-Regí, M.
2013-12-01
The development of magnetic materials for interstitial hyperthermia treatment of cancer is an ever evolving research field which provides new alternatives to antitumoral therapies. The development of biocompatible magnetic materials has resulted in new biomaterials with multifunctional properties, which are able to adapt to the complex scenario of tumoral processes. Once implanted or injected in the body, magnetic materials can behave as thermoseeds under the effect of AC magnetic fields. Magnetic bioceramics aimed to treat bone tumors and magnetic nanoparticles are among the most studied thermoseeds, and supply different solutions for the different scenarios in cancerous processes. This paper reviews some of the biomaterials used for bone cancer treatment and skeletal reinforcing, as well as the more complex topic of magnetic nanoparticles for intracellular targeting and hyperthermia.
Thermoseeds for interstitial magnetic hyperthermia: from bioceramics to nanoparticles.
Baeza, A; Arcos, D; Vallet-Regí, M
2013-12-04
The development of magnetic materials for interstitial hyperthermia treatment of cancer is an ever evolving research field which provides new alternatives to antitumoral therapies. The development of biocompatible magnetic materials has resulted in new biomaterials with multifunctional properties, which are able to adapt to the complex scenario of tumoral processes. Once implanted or injected in the body, magnetic materials can behave as thermoseeds under the effect of AC magnetic fields. Magnetic bioceramics aimed to treat bone tumors and magnetic nanoparticles are among the most studied thermoseeds, and supply different solutions for the different scenarios in cancerous processes. This paper reviews some of the biomaterials used for bone cancer treatment and skeletal reinforcing, as well as the more complex topic of magnetic nanoparticles for intracellular targeting and hyperthermia.
A controlled ac Stark echo for quantum memories.
Ham, Byoung S
2017-08-09
A quantum memory protocol of controlled ac Stark echoes (CASE) based on a double rephasing photon echo scheme via controlled Rabi flopping is proposed. The double rephasing scheme of photon echoes inherently satisfies the no-population inversion requirement for quantum memories, but the resultant absorptive echo remains a fundamental problem. Herein, it is reported that the first echo in the double rephasing scheme can be dynamically controlled so that it does not affect the second echo, which is accomplished by using unbalanced ac Stark shifts. Then, the second echo is coherently controlled to be emissive via controlled coherence conversion. Finally a near perfect ultralong CASE is presented using a backward echo scheme. Compared with other methods such as dc Stark echoes, the present protocol is all-optical with advantages of wavelength-selective dynamic control of quantum processing for erasing, buffering, and channel multiplexing.
New Technique of AC drive in Tokamak using Permanent Magnets
NASA Astrophysics Data System (ADS)
Matteucci, Jackson; Zolfaghari, Ali
2013-10-01
This study investigates a new technique of capturing the rotational energy of alternating permanent magnets in order to inductively drive an alternating current in tokamak devices. The use of rotational motion bypasses many of the pitfalls seen in typical inductive and non-inductive current drives. Three specific designs are presented and assessed in the following criteria: the profile of the current generated, the RMS loop voltage generated as compared to the RMS power required to maintain it, the system's feasibility from an engineering perspective. All of the analysis has been done under ideal E&M conditions using the Maxwell 3D program. Preliminary results indicate that it is possible to produce an over 99% purely toroidal current with a RMS d Φ/dt of over 150 Tm2/s, driven by 20 MW or less of rotational power. The proposed mechanism demonstrates several key advantages including an efficient mechanical drive system, the generation of pure toroidal currents, and the potential for a quasi-steady state fusion reactor. The following quantities are presented for various driving frequencies and magnet strengths: plasma current generated, loop voltage, torque and power required. This project has been supported by DOE Funding under the SULI program.
Guha, Subhendu; Ovshinsky, Stanford R.
1990-02-02
A method of fabricating doped microcrystalline semiconductor alloy material which includes a band gap widening element through a glow discharge deposition process by subjecting a precursor mixture which includes a diluent gas to an a.c. glow discharge in the absence of a magnetic field of sufficient strength to induce electron cyclotron resonance.
Transcranial Alternating Current Stimulation (tACS) Mechanisms and Protocols
Tavakoli, Amir V.; Yun, Kyongsik
2017-01-01
Perception, cognition and consciousness can be modulated as a function of oscillating neural activity, while ongoing neuronal dynamics are influenced by synaptic activity and membrane potential. Consequently, transcranial alternating current stimulation (tACS) may be used for neurological intervention. The advantageous features of tACS include the biphasic and sinusoidal tACS currents, the ability to entrain large neuronal populations, and subtle control over somatic effects. Through neuromodulation of phasic, neural activity, tACS is a powerful tool to investigate the neural correlates of cognition. The rapid development in this area requires clarity about best practices. Here we briefly introduce tACS and review the most compelling findings in the literature to provide a starting point for using tACS. We suggest that tACS protocols be based on functional brain mechanisms and appropriate control experiments, including active sham and condition blinding. PMID:28928634
Study of the AC machines winding having fractional q
NASA Astrophysics Data System (ADS)
Bespalov, V. Y.; Sidorov, A. O.
2018-02-01
The winding schemes with a fractional numbers of slots per pole and phase q have been known and used for a long time. However, in the literature on the low-noise machines design there are not recommended to use. Nevertheless, fractional q windings have been realized in many applications of special AC electrical machines, allowing to improve their performance, including vibroacoustic one. This paper deals with harmonic analysis of windings having integer and fractional q in permanent magnet synchronous motors, a comparison of their characteristics is performed, frequencies of subharmonics are revealed. Optimal winding pitch design is found giving reduce the amplitudes of subharmonics. Distribution factors for subharmonics, fractional and high-order harmonics are calculated, results analysis is represented, allowing for giving recommendations how to calculate distribution factors for different harmonics when q is fractional.
NASA Astrophysics Data System (ADS)
Zarkevich, Nikolai A.; Johnson, Duane D.
2015-03-01
Materials under pressure may exhibit critical electronic and structural transitions that affect equation of states, as known for superconductors and the magneto-structural transformations of iron with both geophysical and planetary implications. While experiments often use constant-pressure (diamond-anvil cell, DAC) measurements, many theoretical results address a constant-volume transitions, which avoid issues with magnetic collapse but cannot be directly compared to experiment. We establish a modified solid-state nudge elastic band (MSS-NEB) method to handle magnetic systems that may exhibit moment (and volume) collapse during transformation. We apply it to the pressure-induced transformation in iron between the low-pressure body-centered cubic (bcc) and the high-pressure hexagonal close-packed (hcp) phases, find the bcc-hcp equilibrium coexistence pressure and a transitional pathway, and compare to shock and DAC experiments. We use methods developed with support by the U.S. Department of Energy (DE-FG02-03ER46026 and DE-AC02-07CH11358). Ames Laboratory is operated for the DOE by Iowa State University under contract DE-AC02-07CH11358.
Analysis of Electrokinetic Mixing Using AC Electric Field and Patchwise Surface Heterogeneities
NASA Astrophysics Data System (ADS)
Luo, Win-Jet; Yarn, Kao-Feng; Hsu, Shou-Ping
2007-04-01
In this paper, the authors investigate the use of an applied AC electric field and microchannel surface heterogeneities to carry out the microfluidic mixing of two-dimensional, time-dependent electroosmotic flows. The time-dependent flow fields within the microchannel are simulated using the backwards-Euler time-stepping numerical method. The mixing efficiencies obtained in microchannels with two different patchwise surface heterogeneity patterns are investigated. In general, the results show that the application of an AC electric field significantly reduces the required mixing length compared with the use of a DC electric field. Furthermore, the presence of oppositely charged surface heterogeneities on the microchannel walls results in the formation of localized flow circulation regions within the bulk flow. These circulation regions grow and decay periodically in accordance with the periodic variation of the AC electric field intensity and provide an effective means of enhancing species mixing in the microchannel. Consequently, the use of an AC electric field together with patchwise surface heterogeneities permits a significant reduction in both the mixing channel length and the retention time required to attain a homogeneous solution.
Accounting for Dark Current Accumulated during Readout of Hubble's ACS/WFC Detectors
NASA Astrophysics Data System (ADS)
Ryon, Jenna E.; Grogin, Norman A.; Coe, Dan A.; ACS Team
2018-06-01
We investigate the properties of excess dark current accumulated during the 100-second full-frame readout of the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) detectors. This excess dark current, called "readout dark", gives rise to ambient background gradients and hot columns in each ACS/WFC image. While readout dark signal is removed from science images during the bias correction step in CALACS, the additional noise from the readout dark is currently not taken into account. We develop a method to estimate the readout dark noise properties in ACS/WFC observations. We update the error (ERR) extensions of superbias images to include the appropriate noise from the ambient readout dark gradient and stable hot columns. In recent data, this amounts to about 5 e-/pixel added variance in the rows farthest from the WFC serial registers, and about 7 to 30 e-/pixel added variance along the stable hot columns. We also flag unstable hot columns in the superbias data quality (DQ) extensions. The new reference file pipeline for ACS/WFC implements these updates to our superbias creation process.